Communication method, device, and system

ABSTRACT

The present invention relates to a communication method, device, and system. The communication method include using low-frequency alternating magnetic field signals to control a communication distance between a first radio frequency (RF) device and second RF device. The communication device receives and uses a first low-frequency alternating magnetic field signal transmitted from a second RF device to control the communication distance to the second RF device. The communication system includes a first RF device and a second RF device. The first RF device generates and transmits a first low-frequency alternating magnetic field signal and receives a second low-frequency alternating magnetic field signal, and the second RF device generates and transmits the second low-frequency alternating magnetic field signal and receives the first low-frequency alternating magnetic field signal. The first RF device and the second RF device control the communication distance using the first and second low-frequency alternating magnetic field signals.

FIELD OF THE INVENTION

The present invention relates to the field of communication and, moreparticularly, relates to a communication system method, a communicationdevice, and a communication system.

BACKGROUND

With the growing popularity of mobile terminals, mobile payments usingmobile terminals has become in high and urgent demands. Although thereare many implementation solutions, these solutions all have theirdisadvantages. Currently, methods adding radio frequency (RF) functionsonto the subscriber identity module (SIM) of a mobile terminal (calledan RF SIM card) or adding a short-distance communication module on themain board of a mobile terminal to achieve a short-distancecommunication of the mobile terminal have been developed. The latershort-distance communication is called near field communication (NFC).These methods have enabled the mobile terminal to become a super smartterminal which can be used to recharge, shop, transact, or verifyidentification. This significantly fulfills the imperious marketdemands.

The short-distance solution based on the mobile-terminals with RF SIMcards has attracted extensive attentions because of its simplicity andno need to modify the mobile terminals. In such solution, the RF SIMcard uses an ultra-high frequency (UHF) technology. Because the UHF SIMcard, especially the SIM card using a 2.4 GHz·ISM public frequency range(i.e., the industry, science, and medical frequency), has a very highworking frequency, and the size of antenna is small, RF signals withsufficient strength can be generated by putting a small antenna in a SIMcard. Thus, even when the SIM card is installed inside a mobileterminal, the RF signals can still emit from the mobile terminal. Anindustry-widely-used RF transceiver chip installed in a card reader canreliably receive RF signals from a majority of the mobile terminalswithout extra amplification. Thus, this can enable the mobile terminalsto achieve the short-distance communication function without modifyingthe existing mobile terminals. However, current technologies often failto effectively control the communication distance between the RF cardand a card reader.

SUMMARY OF THE INVENTION

The present invention provides a communication method, a communicationdevice, and a communication system to solve the problems of prior art asbeing unable to effective control RF communication distance.

To solve such problems, the present invention provides the followingtechnical solutions.

A communication method includes controlling a communication distancebetween a first radio frequency (RF) device and a second RF device usinga low-frequency magnetic field; and exchanging information between thefirst RF device and the second RF device within a predetermined distancerange using RF channels.

In one embodiment, one of the first RF device and the second RF devicereceives a first low-frequency alternating magnetic field signal fromthe other of the first RF device and the second RF device to controlcommunication distance between the first RF device and the second RFdevice.

In one embodiment, receiving the first low-frequency alternatingmagnetic signal to control the communication distance further includesdetecting the received first low-frequency alternating magnetic fieldsignal; converting the first low-frequency alternating magnetic fieldsignal into a first electrical signal; comparing the first electricalsignal with a first preset threshold value; and controlling thecommunication distance between the first RF device and second RF devicebased on a comparison result.

In one embodiment, when the first electrical signal is greater than orequal to the first preset threshold value, determining that the first RFdevice and second RF device are within the predetermined distance range.

In one embodiment, the first low-frequency alternating magnetic fieldsignal is related to a frequency f0 and, when a frequency of firstlow-frequency alternating magnetic field signal is less than or equal tothe frequency f0, the first RF device and the second RF device arewithin a valid distance range.

In one embodiment, the first RF device is a card reader, the second RFdevice is a card, and the frequency f0 is determined by: determining adistance control target (Din, Dv) based on the first low-frequencyalternating magnetic field signal, wherein Din represents a distance inwhich, within a range of 0-Din, card transaction is ensured, and Dvrepresents a distance fluctuation range in which, within Din˜(Din+Dv),card transaction is allowed and, beyond Din+Dv, card transaction is notallowed; determining a detection voltage fluctuation range δ_(R) of thecard reader; determining a detection voltage fluctuation range δ_(C) ofthe card; determining voltage-distance curves of the plurality typicalterminals and obstacles at the frequency f of first low-frequencyalternating magnetic field signal; based on the distance control target(Din, Dv), determining a detection voltage fluctuation range δ_(A) ofthe card reader, the range δ_(A) being equal to a difference between avoltage corresponding to a distance point Din on a voltage-distancecurve with an average field intensity attenuation curve slope andobtained from the voltage-distance curves of the plurality of typicalterminals and obstacles and the voltage corresponding to a distancepoint (Din+Dv); determining a detection voltage fluctuation range δ_(T)of the of the card caused by a mobile terminal containing the card, theparameter δ_(T) representing a fluctuation range of a detection voltageof the card caused by attenuation characteristics of the mobile terminaland δ_(T)=δ_(A)−δ_(R)−δ_(C); calculating a maximum field intensitydifference δ at various distances with distance control range of varioustypical terminals and obstacles; if δ is greater than δ_(T), decreasingthe frequency f and continuing from the step of determining thevoltage-distance curves; if δ is less than δ_(T), increasing thefrequency f and continuing from the step of determining thevoltage-distance curves; and if δ is equal to δ_(T), determining thecurrent frequency f is the frequency f0.

In one embodiment, the modulation mode, the coding mode, and thetransmission magnetic flux density Bc of the first low-frequencyalternating magnetic field signal is selected by: selecting a codingmode without an average DC component; selecting no modulation or acarrier modulation mode without amplitude change; selecting thetransmission magnetic flux density Bc by: under a selected operatingfrequency that is less than f0, a selected modulation and a selectedcoding mode, selecting magnetic detection and the amplification gainthat are easy to achieve by the card reader; detecting an inherent noisevoltage amplitude Vn of the detection voltage of the card reader when nolow-frequency alternating magnetic field signal; detecting the detectionvoltage Vr of the card reader when the card reader is sending thelow-frequency alternating magnetic field signal using the selectedmodulation and coding mode; and selecting the transmission magnetic fluxdensity Bc such that such that Vr/Vn>SNR, where SNR issignal-to-noise-ratio of the card reader.

In one embodiment, the encoding mode of the first low-frequencyalternating magnetic field signal is a Manchester code, a DifferentialManchester code, or an NRZ code.

In one embodiment, the modulation of the first low-frequency alternatingmagnetic field signal is an on-off keying modulation, a phase shiftkeying modulation, or a frequency shift keying modulation.

In one embodiment, the first electrical signal is a voltage signal, thefirst threshold value is a voltage threshold Vt, and the voltagethreshold Vt is determined by: under selected transmission parameters,measuring voltage-distance curves of a plurality of typical terminalsand obstacles, the selected transmission parameters including afrequency of the low-frequency alternating magnetic field signal, amodulation mode, a coding mode, and a transmission magnetic flux densityBr; and obtaining a reference voltage-distance curve, the referencevoltage-distance curve being a average value of curves of the typicalterminals and obstacles; and selecting a voltage value at a distancepoint at half of a maximum valid card transaction range on the referencevoltage-distance curve as Vt for the card reader.

In one embodiment, the frequency of the low-frequency alternatingmagnetic field signal is in a range of approximately 300 Hz˜50 KHz.

In one embodiment, the frequency of the low-frequency alternatingmagnetic field signal is one of 10 KHz, 15 KHz, 20 KHz, 25 KHz, and 30KHz.

In one embodiment, the one of the first RF device and the second RFdevice sends a second low-frequency alternating magnetic field signal tothe other of the first RF device and the second RF device withcommunication distance confirmation information.

In one embodiment, one of the first RF device and the second RF devicesends a first low-frequency alternating magnetic field signal to theother of the first RF device and the second RF device, and receives asecond low-frequency alternating magnetic field signal from the other ofthe first RF device and the second RF device; and identificationinformation carried in the second low-frequency alternating magneticfield signal is used to control communication distance between the firstRF device and the second RF device.

In one embodiment, when the identification information in the secondlow-frequency alternating magnetic field signal is the same asidentification information of the one of the first RF device and thesecond RF device sending the first low-frequency alternating magneticfield signal, it is determined that the first RF device and the secondRF device are within a valid distance range.

In one embodiment, one of the first RF device and the second RF deviceconverts the second low-frequency alternating magnetic field signal intoa second electrical signal and compares the second electrical signalwith a second preset threshold; and when the second electrical signal isgreater than or equal to the second preset threshold and theidentification information in the second low-frequency alternatingmagnetic field signal is the same as identification information of theone of the first RF device and the second RF device sending the firstlow-frequency alternating magnetic field signal, it is determined thatthe first RF device and the second RF device are within a valid distancerange.

In one embodiment, the other of the first RF device and the second RFdevice controls the communication distance between the first RF deviceand the second RF device based on received first low-frequencyalternating magnetic field signal and, when it is considered that thefirst RF device and the second RF device are within a valid distancerange, sends back the second low-frequency alternating magnetic fieldsignal.

In one embodiment, the other of the first RF device and the second RFdevice controlling the communication distance between the first RFdevice and the second RF device based on received first low-frequencyalternating magnetic field signal further includes: converting the firstlow-frequency alternating magnetic field signal into a first electricalsignal; comparing the first electrical signal with a first presetthreshold value; and controlling the communication distance between thefirst RF device and second RF device based on a comparison result.

In one embodiment, when the first electrical signal is greater than orequal to the first preset threshold value, determining that the first RFdevice and second RF device are within the predetermined distance range.

In one embodiment, the first RF device is a card reader, the second RFdevice is a card, the first low-frequency alternating magnetic fieldsignal is related to a frequency f0 and, when a frequency of firstlow-frequency alternating magnetic field signal is less than or equal tothe frequency f0, mobile terminals equipped with the second RF deviceare within a valid distance range, the frequency f0 is determined by:determining a distance control target (Din, Dv) based on the firstlow-frequency alternating magnetic field signal, wherein Din representsa distance in which, within a range of 0-Din, card transaction isensured for the mobile terminals equipped with the second RF device, andDv represents a distance fluctuation range in which, withinDin˜(Din+Dv), card transaction is allowed and, beyond Din+Dv, cardtransaction is not allowed; determining a detection voltage fluctuationrange δ_(R) of the second RF device caused by the first RF device;determining a detection voltage fluctuation range δ_(C) caused by thesecond RF device; determining voltage-distance curves of the pluralitytypical terminals and obstacles at the frequency f of firstlow-frequency alternating magnetic field signal; based on the distancecontrol target (Din, Dv), determining a detection voltage fluctuationrange δ_(A) of the second RF device, the range δ_(A) being equal to adifference between a voltage corresponding to a distance point Din on avoltage-distance curve with an average field intensity attenuation curveslope and obtained from the voltage-distance curves of the plurality oftypical terminals and obstacles and the voltage corresponding to adistance point (Din+Dv); determining a detection voltage fluctuationrange δ_(T) of the second RF device caused by a mobile terminalcontaining the second RF device, the parameter δ_(T) representing afluctuation range of a detection voltage of the card caused byattenuation characteristics of the mobile terminal andδ_(T)=δ_(A)−δ_(R)−δ_(C); calculating a maximum field intensitydifference δ at various distances with distance control range of varioustypical terminals and obstacles; if δ is greater than δ_(T), decreasingthe frequency f and continuing from the step of determining thevoltage-distance curves; if δ is less than δ_(T), increasing thefrequency f and continuing from the step of determining thevoltage-distance curves; and if δ is equal to δ_(T), determining thecurrent frequency f is the frequency f0.

In one embodiment, the first RF device is a card reader, the second RFdevice is a card, the second low-frequency alternating magnetic fieldsignal is related to a frequency f0′ and, when a frequency of secondlow-frequency alternating magnetic field signal is less than or equal tothe frequency f0′, mobile terminals equipped with the second RF deviceare within a valid distance range, the frequency f0′ is determined by:determining a distance control target (Din, Dv′) based on the secondlow-frequency alternating magnetic field signal, wherein Din representsa distance in which, within a range of 0-Din, card transaction isensured for the mobile terminals equipped with the second RF device, andDv′ represents a distance fluctuation range in which, withinDin˜(Din+Dv′), card transaction is allowed and, beyond Din+Dv′, cardtransaction is not allowed; determining a detection voltage fluctuationrange δ_(R) of the first RF device caused by the second RF device;determining a detection voltage fluctuation range δ_(C) caused by thefirst RF device; determining voltage-distance curves of the pluralitytypical terminals and obstacles at the frequency f′ of secondlow-frequency alternating magnetic field signal; based on the distancecontrol target (Din, Dv′), determining a detection voltage fluctuationrange δ_(A)′ of the first RF device, the range δ_(A)′ being equal to adifference between a voltage corresponding to a distance point Din on avoltage-distance curve with an average field intensity attenuation curveslope and obtained from the voltage-distance curves of the plurality oftypical terminals and obstacles and the voltage corresponding to adistance point (Din+Dv′); determining a detection voltage fluctuationrange δ_(T)′ caused by a mobile terminal containing the second RFdevice, the parameter δ_(T)′ representing a fluctuation range of adetection voltage of the card caused by attenuation characteristics ofthe mobile terminal and δ_(T)′=δ_(A)′−δ_(R)′−δ_(C)′; and calculating amaximum field intensity difference δ′ at various distances with distancecontrol range of various typical terminals and obstacles; if δ′ isgreater than δ_(T)′, decreasing the frequency f and continuing from thestep of determining the voltage-distance curves; if δ′ is less thanδ_(T)′, increasing the frequency f and continuing from the step ofdetermining the voltage-distance curves; and if δ′ is equal to δ_(T)′,determining the current frequency f′ is the frequency f0′.

In one embodiment, the modulation mode, the coding mode, and thetransmission magnetic flux density Br of the first low-frequencyalternating magnetic field signal is selected by: selecting a codingmode without an average DC component; selecting no modulation or acarrier modulation mode without amplitude change; selecting thetransmission magnetic flux density Br by: under a selected operatingfrequency that is less than f0, a selected modulation and a selectedcoding mode, selecting a typical noise mobile terminal and magneticdetection and the amplification gain that are easy to achieve in thesecond RF device; detecting an inherent noise voltage amplitude Vn ofthe detection voltage of the second RF device when no low-frequencyalternating magnetic field signal; detecting the detection voltage Vc ofthe second RF device when the first RF device is sending thelow-frequency alternating magnetic field signal using the selectedmodulation and coding mode; and selecting the transmission magnetic fluxdensity Br such that such that Vc/Vn>SNR, where SNR issignal-to-noise-ratio of the second RF device.

In one embodiment, the encoding mode of the first low-frequencyalternating magnetic field signal is a Manchester code, a DifferentialManchester code, or an NRZ code.

In one embodiment, the modulation of the first low-frequency alternatingmagnetic field signal is an on-off keying modulation, a phase shiftkeying modulation, or a frequency shift keying modulation.

In one embodiment, the modulation mode, the coding mode, and thetransmission magnetic flux density Bc of the second low-frequencyalternating magnetic field signal is selected by: selecting a codingmode without an average DC component; selecting no modulation or acarrier modulation mode without amplitude change; selecting thetransmission magnetic flux density Bc by: under a selected operatingfrequency that is less than f0′, the selected modulation and theselected coding mode, selecting a typical noise terminal and magneticdetection and the amplification gain that are easy to achieve by thefirst RF device; detecting an inherent noise voltage amplitude Vn′ ofthe detection voltage of the first RF device when no low-frequencyalternating magnetic field signal; detecting the detection voltage Vr ofthe first RF device when the mobile terminal is sending thelow-frequency alternating magnetic field signal using the selectedmodulation and coding mode; and selecting the transmission magnetic fluxdensity Bc such that such that Vr/Vn′>SNR′, where SNR′ issignal-to-noise-ratio of the first RF device.

In one embodiment, the frequency of each of the first low-frequencyalternating magnetic field signal and the second low-frequencyalternating magnetic field signal is in one of a low frequency band, avery-low frequency band, and an ultra-low frequency band, wherein theultra-low frequency band is a range of approximately 300 Hz˜3000 Hz, thevery-low frequency band is in a range of approximately 3 KHz˜30 KHz, andthe low frequency band is in a range of approximately 30 KHz˜300 KHz.

In one embodiment, the frequency of each of the first low-frequencyalternating magnetic field signal and the second low-frequencyalternating magnetic field signal is in a range of approximately 300Hz˜50 KHz.

In one embodiment, the frequency of the low-frequency alternatingmagnetic field signal is one of 500 Hz, 1 KHz, 1.5 KHz, 2 KHz, 2.5 KHz,3 KHz, 4 KHz, 5 KHz, 10 KHz, 20 KHz, and 30 KHz.

In one embodiment, the frequency of the low-frequency alternatingmagnetic field signal is one of 10 KHz, 15 KHz, 20 KHz, 25 KHz, and 30KHz.

A radio frequency (RF) device includes a magnetic signal receiver moduleconfigured to receive a first low-frequency alternating magnetic fieldsignal of another RF device; a main control module configured to controla communication distance between the RF device and the another RFdevice; and an RF transceiver module configured to exchange data withthe another RF device within a predetermined distance range.

In one embodiment, the main control module is further configured to:convert the first low-frequency alternating magnetic field signal into afirst electrical signal; to compare the first electrical signal with afirst preset threshold value; and to control the communication distancebetween the first RF device and second RF device based on a comparisonresult.

In one embodiment, the magnetic signal receiver module includes anamplifier circuit, a filter circuit, and a decoding circuit,sequentially connected; the filter circuit is connected to a couplingcoil in the RF device; and the decoding circuit is connected to the maincontroller; the amplifier circuit is configured to amplify a firstelectrical signal converted from the first low-frequency alternatingmagnetic field signal received by the coupling coil; the filter circuitis configured to filter the amplified first electrical signal and tosuppress noise and interference outside a valid signal frequency band;the decoding circuit is configured to decode the filtered signal basedon the coding mode of the RF device sending the first low-frequencyalternating magnetic field signal and to send the decoded signal to themain controller.

In one embodiment, the magnetic signal receiver module further includesa demodulation circuit disposed between the filter circuit and thedecoding circuit and configured to demodulate the filtered signal basedon a modulation scheme used by the another RF device and to send thedemodulated signal to the decoding circuit.

In one embodiment, the magnetic signal receiver module includes anamplifier circuit and a filter circuit, sequentially connected; thefilter circuit is connected to a coupling coil in the RF device; and thedecoding circuit is connected to the main controller; the amplifiercircuit is configured to amplify a first electrical signal convertedfrom the first low-frequency alternating magnetic field signal receivedby the coupling coil; the filter circuit is configured to filter theamplified first electrical signal and to suppress noise and interferenceoutside a valid signal frequency band; the main controller is furtherconfigured to decode the filtered signal based on the coding mode of theRF device sending the first low-frequency alternating magnetic fieldsignal.

In one embodiment, the magnetic signal receiver module further includesa demodulation circuit disposed between the filter circuit and the maincontroller and configured to demodulate the filtered signal based on amodulation scheme used by the another RF device and to send thedemodulated signal to the main controller.

In one embodiment, the RF transceiver module includes an RF transceiver,an impedance matching network, and an RF antenna, sequentiallyconnected, and the RF transceiver is connected to the main controller.

In one embodiment, the RF device further includes a magnetic signaltransmitting module configured to transmit the communication distanceconfirmation information to the another RF device.

In one embodiment, the magnetic signal transmitting module includes anencoder circuit, a modulation circuit, a D/A converter circuit, and adrive circuit, sequentially connected, the encoder circuit is connectedto the main controller, and the drive circuit is connected to thecoupling coil in the RF device; the main controller is configured togenerate information carried in the second low-frequency alternatingmagnetic field signal to be transmitted by the RF device, the secondlow-frequency alternating magnetic field signal information being adigital baseband signal; the encoder circuit is configured to encode thedigital baseband signal provided by the main controller; the D/Aconverter circuit is configured to convert the encoded digital signalinto a low-frequency analog signal; and the drive circuit is configuredto amplify the low-frequency analog signal and to drive the couplingcoil to generate the second low-frequency alternating magnetic field.

In one embodiment, the magnetic signal transmitting module furtherincludes a modulation circuit disposed between the main controller andthe D/A converter circuit; and the modulation circuit is configured tomodulate the encoded data and to send the modulated data to the D/Aconverter circuit.

In one embodiment, the magnetic signal transmitting module furtherincludes a modulation circuit disposed between the main controller andthe D/A converter circuit; and the modulation circuit is configured tomodulate the encoded digital baseband signal and to send the modulatedsignal to the D/A converter circuit.

In one embodiment, the magnetic signal transmitting module includes aD/A converter circuit and a drive circuit, sequentially connected, theD/A converter circuit is connected to the main controller, and the drivecircuit is connected to the coupling coil in the RF device; the maincontroller is configured to generate low-frequency encoded data and tosend the data to the D/A converter circuit; the D/A converter circuit isconfigured to convert the low-frequency encoded data into alow-frequency analog signal; and the drive circuit is configured toamplify the low-frequency analog signal and to drive the coupling coilto generate the second low-frequency alternating magnetic field.

In one embodiment, the magnetic signal receiver module and the magneticsignal transmitting module perform two-way communication with the RFdevice transmitting the first low-frequency alternating magnetic fieldsignal through a time-division duplex mode or a frequency-divisionduplex mode; and an operating frequency of the magnetic signal receivermodule and an operating frequency of the magnetic signal transmittingmodule both less than a predetermined maximum operating frequency.

A communication system comprises a first radio frequency (RF) device andsecond RF device, the first RF device and the second RF device control acommunication distance using low-frequency alternating magnetic fieldsignals and exchange information between the first RF device and thesecond RF device using RF channels, the first RF device furtherincludes: a first magnetic signal transceiver configured to generate andtransmit a first low-frequency alternating magnetic field signal and toreceive a second low-frequency alternating magnetic field signal; afirst RF communication unit configured to exchange information with thesecond RF device; the second RF device further includes: a secondmagnetic signal transceiver configured to generate and transmit thesecond low-frequency alternating magnetic field signal and to receivethe first low-frequency alternating magnetic field signal; a second RFcommunication unit configured to exchange information with the first RFcommunication unit.

In one embodiment, the first magnetic signal transceiver furtherincludes a first magnetic signal receiving unit and a first magneticsignal transmitting unit; the first magnetic signal transmitting unit isconfigured to transmit the first low-frequency alternating magneticfield signal; and the first magnetic signal receiving unit is configuredto receive the second low-frequency alternating magnetic field signal;the second magnetic signal transceiver further includes a secondmagnetic signal receiving unit and a second magnetic signal transmittingunit; the second magnetic signal transmitting unit is configured totransmit the second low-frequency alternating magnetic field signal; andthe second magnetic signal receiving unit is configured to receive thefirst low-frequency alternating magnetic field signal.

In one embodiment, the first magnetic signal transceiver includes afirst modulation unit, and the first modulation unit is configured toadd identification information of the first RF device into the firstlow-frequency alternating magnetic field signal; and the second magneticsignal transceiver includes a second modulation unit, and the secondmodulation unit is configured to add identification information of thesecond RF device into the second low-frequency alternating magneticfield signal.

In one embodiment, the first magnetic signal transceiver includes afirst determination unit, and the first determination unit is configuredto determine whether the first RF device enters into the preset validcard transaction range between the second RF device and the first RFdevice, based on the second low-frequency alternating magnetic fieldsignal detected by the first RF device; and the second magnetic signaltransceiver includes a second determination unit, and the seconddetermination unit is configured to determine whether the second RFdevice enters into the preset valid card transaction range between thefirst RF device and the second RF device, based on the firstlow-frequency alternating magnetic field signal detected by the secondRF device; when the second determination unit determines that the secondRF device enters into the preset valid card transaction range betweenthe first RF device and the second RF device, and when the firstdetermination unit determines that the first RF device enters into thepreset valid card transaction range between the second RF device and thefirst RF device, it is determined that the distance between the first RFdevice and the second RF device is within the predetermined effectivecommunication distance range.

In one embodiment, the first determination unit includes a firstcomparison sub-unit and a first determination sub-unit, the firstcomparison sub-unit is configured to compare the identificationinformation of the first RF device demodulated from the secondlow-frequency alternating magnetic field signal with its ownidentification information; and the first determination sub-unit isconfigured to, based on a comparison result, determine whether the firstRF device enters into a predetermined valid distance range between thesecond RF device and the first RF device; and the second determinationunit includes a second comparison sub-unit and a second determinationsub-unit, the second comparison sub-unit is configured to compare theelectrical signal converted from the first low-frequency alternatingmagnetic field signal with the preset threshold value, and the seconddetermination sub-unit is configured to, based on a comparison result,determine whether the second RF device enters into a predetermined validdistance range between the second RF device and the first RF device.

In one embodiment, the first judgment unit includes a third comparisonsub-unit and a third determination sub-unit, the third comparisonsub-unit is configured to compare a second electrical signal convertedfrom the second low-frequency alternating magnetic field signal with asecond threshold value, and the third determination sub-unit isconfigured to, based on a comparison result, determine whether thesecond RF device enters into the predetermined valid distance rangebetween the second RF device and the first RF device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of an RF device according to thepresent invention;

FIG. 2 illustrates a block diagram of an RF SIM card according to thepresent invention;

FIG. 3 illustrates a block diagram of a specific configuration of themagnetic signal transmitter module, magnetic signal receiver module, andRF data transceiver module inside an RF SIM card of FIG. 2;

FIG. 4 illustrates a planar structural diagram of the RF SIM cardaccording to the present invention;

FIG. 5 illustrates an exemplary implementation where the low-frequencyreceiving channel and transmitting channel of the SIM card share acoupling coil and the low-frequency receiving channel and transmittingchannel are switched by an analog switch;

FIG. 6 illustrates a use scenario of an RF SIM card according to thepresent invention;

FIG. 7 is a flowchart of an application of the RF SIM card according tothe present invention;

FIG. 8 illustrates a block diagram of a selection system to select themaximum operating frequency f0 of a low-frequency channel according tothe present invention;

FIG. 9 illustrates the total received detection voltage fluctuationrange δ_(A) determined by the distance control target (Din, Dv);

FIG. 10 illustrates voltage-distance curves and fluctuation range δ of atypical terminal and obstacle;

FIG. 11 illustrates detection voltage signal detected by the card readerfor directly-transmitted baseband signal without modulation and thevoltage waveform diagram of the detected voltage signal for a sine-waveFSK modulation;

FIG. 12 illustrates a calculation method for a referencevoltage-distance curve of the low-frequency channel;

FIG. 13 illustrates a block diagram of an overall structure of acommunication system;

FIG. 14 illustrates a specific configuration of the magnetic signalreceiver 711 and the magnetic signal transmitter 721;

FIG. 15 illustrates a detailed structural diagram of a communicationsystem;

FIG. 16 illustrates a schematic diagram of the low-frequency transmitterpart of the RF card;

FIG. 17 illustrates a low-frequency data frame transmitted by the RFcard;

FIG. 18 illustrates a block diagram of an overall structure of an RFcard reader;

FIG. 19 illustrates a structural block diagram of a selection system forselecting the maximum operating frequency f0 of the first low-frequencychannel;

FIG. 20 illustrates the total received detection voltage fluctuationrange δ_(A) determined by the distance control target (Din, Dv);

FIG. 21 illustrates voltage-distance curves and fluctuation range δ of atypical terminal and obstacle;

FIG. 22 illustrates five voltage-distance curves of five typical mobileterminals at frequency f of 3.3 KHz;

FIG. 23 illustrates a detection voltage signal detected by the RF cardfor directly-transmitted baseband signal without modulation and thevoltage waveform diagram of the detected voltage signal for a sine-waveFSK modulation;

FIG. 24 illustrates a block diagram of a system for detecting thevoltage-distance curves under the second low-frequency channelcommunication mode;

FIG. 25 illustrates voltage-distance curves detected by the system inFIG. 24;

FIG. 26 illustrates a diagram of an exemplary communication system;

FIG. 27 illustrates a low-frequency data frame transmitted by the RFcard reader;

FIG. 28 illustrates a low-frequency data frame transmitted by the RFcard;

FIG. 29 illustrates a structural diagram of an RF reader;

FIG. 30 illustrates typical forms of the DC and AC magnetic field withpeak field intensity constant amplitude;

FIG. 31 illustrates a typical low-frequency AC magnetic field withdifferential field intensity constant amplitude;

FIG. 32 illustrates a flowchart of a selection process for thetransmission parameters;

FIG. 33 illustrates an exemplary RF card reader error correction system;

FIG. 34 illustrates a configuration using an analog switch to switchoperation when the low-frequency receiver coil and the low-frequencytransmitter coil share the same coil;

FIG. 35 illustrates a structural block diagram of a selection system forselecting the maximum operating frequency f0 of the first low-frequencychannel;

FIG. 36 illustrates the total received detection voltage fluctuationrange δ_(A) determined by the distance control target (Din, Dv);

FIG. 37 illustrates voltage-distance curves and fluctuation range δ of atypical terminal and obstacle;

FIG. 38 illustrates five voltage-distance curves of five typical mobileterminals at frequency f of 3.3 KHz;

FIG. 39 illustrates a detection voltage signal detected by the second RFdevice for directly-transmitted baseband signal without modulation andthe voltage waveform diagram of the detected voltage signal for asine-wave FSK modulation;

FIG. 40 illustrates a calculation method of a reference voltage-distancecurve under the first low-frequency channel communication mode;

FIG. 41 illustrates a block diagram of a system for detecting thevoltage-distance curves under the second low-frequency channelcommunication mode;

FIG. 42 illustrates the voltage-distance curves detected by the systemin FIG. 41;

FIG. 43 illustrates a corresponding relationship between the totaldistance fluctuation range of the system and the total receiveddetection voltage fluctuation range of the first RF device under thesecond low-frequency channel communication mode;

FIG. 44 illustrates a voltage-distance curves and fluctuation range δ′of a typical terminal and obstacle under the second low-frequencychannel communication mode;

FIG. 45 illustrates a block diagram of an overall structure of acommunication system;

FIG. 46 illustrates a specific configuration of first magnetic signaltransceiver 711 and second magnetic signal transceiver 721 of FIG. 45;

FIG. 47 illustrates a specific configuration diagram of firstdetermination unit 7112 and second determination unit 7212 of FIG. 46;

FIG. 48 illustrates a detailed structural diagram of a communicationsystem;

FIG. 49 illustrates a schematic diagram of the low-frequency transmitterpart of the first RF device;

FIG. 50 illustrates a low-frequency data frame transmitted by the firstRF device;

FIG. 51 illustrates a low-frequency data frame transmitted by the secondRF device.

DETAILED DESCRIPTION OF THE INVENTION Embodiment One

As shown in FIG. 1, a radio frequency (RF) device 10 includes an RF datatransceiver module 102, and also includes a magnetic signal receivingmodule 105 for receiving a first low-frequency alternating magneticfield signal emitted by another RF device; a main control module 101 forcontrolling the communication distance between the RF device 10 andanother RF device according to the first low-frequency alternatingmagnetic field signal. The RF data transceiver module 102 is used by theRF device 10 to exchange information with another RF device within apreset distance range.

That is, the RF device 10 controls the communication distance with theanother RF device through the first low-frequency alternating magneticfield signal, and the RF device 10 exchanges information with theanother RF device via the RF data transceiver module 102. The other RFdevice may be an RF card reader. Further, the RF device 10 may be an RFcard (e.g., a SIM card, a UIM card, a USIM card, a TF card, or an SDcard), may be placed in a mobile terminal, or may be a built-in RF card.The mobile terminal may include a mobile phone, a personal digitalassistant PDA, an MP4 or a laptop computer, etc.

The RF device 10 is further described in detail using an SIM card as anexample. As shown in FIG. 2, an RF SIM card 100 with two-waylow-frequency communication functionality is provided. The RF SIM card100 includes a main controller 101 a, the RF data transceiver module102, a coupling coil 103, a magnetic signal transmitting module 104, amagnetic signal receiving module 105, an SIM card microcontroller 106,and an SIM card interface module 107.

The magnetic signal receiving module 105 receives a first low-frequencyalternating magnetic field signal through the coupling coil 103 andsends the received signal to the main controller 101 a. The magneticsignal transmitting module 104 is used to generate and transmit throughthe coupling coil section 103 a second low-frequency alternatingmagnetic field signal, the second low-frequency alternating magneticfield signal is used to send RF communication distance confirmationinformation to the RF card reader transmitting the first low-frequencyalternating magnetic field signal.

The first low-frequency alternating magnetic field signal may carryidentification information of the RF card reader transmitting the firstlow-frequency alternating magnetic field signal. The secondlow-frequency alternating magnetic field signal may carry theidentification information of the RF SIM card 100. The magnetic signalreceiving module 105 and the magnetic signal transmission module 104 mayperform two-way communication with the RF card reader transmitting thefirst low-frequency alternating magnetic field signal through atime-division duplex mode or a frequency-division duplex mode.

As shown in FIG. 3, the magnetic signal receiving module 105 mayincludes an amplifier circuit 1051, a filter circuit 1052, ademodulation circuit 1053, and a decoder circuit 1054, sequentiallyconnected with one another. The amplifier circuit 1051 is also connectedto the coupling coil 103, and the decoder circuit 1054 is also connectedto the main controller 101 a. The demodulation circuit 1053 may beoptional and, when the first low-frequency magnetic signal received isan un-modulated baseband signal, the filter circuit 1052 may be directlyconnected to the decoder circuit 1054.

The coupling coil 103 is inductive to and receives the firstlow-frequency magnetic signal carrying the identification information ofthe RF card reader, which is generated by the RF card reader, andconverts the received magnetic signal to a first electrical signal. Theamplifier circuit 1051 performs amplification processing on the firstelectrical signal reflecting changes of the magnetic field intensity,and increases and adjusts the signal amplitude within a predeterminedrange. The filter circuit 1052 performs filtering processing on theamplified first electrical signal, and suppresses noise and interferenceoutside a useful signal frequency band. The demodulation circuit 1053performs demodulation processing on the filtered signal according to themodulation scheme used by the RF card reader. The decoder circuit 1054performs corresponding decoding processing according to the codingscheme used by the RF card reader. Finally, the main controller 101 a isconfigured to further process the digital baseband signal obtained bythe above processes, to determine the inductive magnetic field intensitybased on the signal amplitude, and to determine whether the one-waycommunication distance from the RF card reader to the mobile terminalhaving the RF SIM card 100. Meanwhile, the main controller 101 a mayobtain the identification information of the RF card reader carried inthe baseband signal and determine whether to trigger a next stepoperation.

The amplifier circuit 1051 may be a unilateral amplifier circuit ordifferential amplifier circuit or a fully differential amplifiercircuit, and the gain may be adjusted flexibly according to thecommunication distance. The filter circuit 1052 may use an analogband-pass filter structure, a passive RC filter structure, or an activefilter structure with an operational amplifier or a dedicated filter IC,and its bandwidth may be determined based on the center frequency of thelow-frequency magnetic signal and the upper and lower cut-off frequencymay also be adjusted flexibly. The demodulation circuit 1053 and thedecoder circuit 1054 may be determined based on the modulation schemeand the coding mode of the received low-frequency magnetic signal.

The decoder circuit 1054 may use a corresponding dedicated IC to realizethe decoding by hardware, or the main controller 101 a may use internalsoftware to realize the decoding. When the decoder circuit 1054 usesdedicated IC hardware to realize the decoding, the connection betweenthe decoder circuit 1054 and the main controller 101 a may be asingle-line serial mode, or a multi-line parallel mode. When the decodercircuit 1054 uses internal software to realize the decoding, thereceived first low-frequency magnetic induction signal, afteramplifying, filtering, and demodulation (if necessary), is directly sentto the main controller 101 a.

Further, the magnetic signal transmitting module 104 includes an encodercircuit 1044, a modulation circuit 1043, a D/A converter circuit 1042,and a drive circuit 1041, sequentially connected with one another. Theencoder circuit 1044 is also connected to the main controller 101 a, andthe drive circuit 1041 is also connected to the coupling coil 103. Themodulation circuit 1043 can be adjusted according to actual need and,when only the baseband signal is transmitted in order to simplify thesignaling link, the encoder circuit 1044 may be directly connected withthe D/A converter circuit 1042.

The main controller 101 a is used to generate information carried in thesecond low-frequency magnetic signal to be transmitted by the SIM card100. The information may be a digital baseband signal. The encodercircuit 1044 is used to perform certain encoding processing on thedigital baseband signal provided by the main controller 101 a, and theencoding scheme may depend on system requirements. The modulationcircuit 1043 is used to perform certain modulation processing on theencoded digital baseband signal, and the modulation format may depend onthe system requirements. The D/A converter circuit 1042 is used toconvert the encoded and modulated digital signal into a low-frequencyanalog signal. The drive circuit 1041 is used to amplify thelow-frequency analog signal and to drive the coupling coil 103 togenerate a low-frequency alternating magnetic field to transmit thesecond low-frequency magnetic induction signal.

The encoder circuit 1044 may choose any appropriate coding schemewithout a DC component, such as Manchester encoding, differentialManchester encoding, alternate mark inversion code (AMI), third-orderhigh-density bipolar code (HDB3), or Miller code (Miller), etc. Themodulation circuit 1043 may use any appropriate digital modulationformat without amplitude change, such as on-off keying (OOK), frequencyshift keying (FSK), binary phase shift keying (BPSK), quadrature phaseshift keying (QPSK), or other digital modulation format. The carrierwaveform may be select as one of a sine waveform, a triangular waveform,or a square waveform. Further, with respect to the D/A converter circuit1042, the digital input can be a serial input or parallel inputs, andthe analog output can be a single-sided or differential current orvoltage waveform outputs. The conversion accuracy and conversion ratiocan be configured based on system performance requirements. The drivecircuit 1041 may be a multi-stage amplifier circuit containing at leastone stage of amplification, and may be formed by integrated operationalamplifiers or by discrete transistors, the gain can be adjustedaccording to real needs.

The encoder circuit 1044 may use a corresponding dedicated IC to realizethe encoding by hardware, or the main controller 101 a may use internalsoftware to realize the encoding. When the encoder circuit 1044 usesdedicated IC hardware to realize the encoding, the connection betweenthe encoder circuit 1044 and the main controller 101 a may be asingle-line serial mode, or a multi-line parallel mode. When the encodercircuit 1044 uses internal software to realize the encoding, thelow-frequency encoded signal generated by the main controller 101 a isdirectly sent to the modulation circuit 1043 (if necessary), or to theD/A converter circuit.

The RF data transceiver module 102 includes an RF transceiver 1023,impedance matching network 1022, and an RF antenna 1021, sequentiallyconnected. The RF transceiver 1023 is connected with the main controller101 a via a serial bus interface, which may be any appropriate bussupporting a full-duplex or half-duplex communication bus mode, such asa serial peripheral bus (SPI) interface, or a Universal AsynchronousReceiver Transmitter (UART) interface. The impedance matching network1022 is used to connect the RF transceiver 1023 and the RF antenna 1021and to ensure the maximum power transmission of the RF signalstransmitted or received in the communication link. The RF antenna 1021is used to radiate electromagnetic energy to external space and toreceive the electromagnetic field from the external space. The RFantenna may be a monopole antenna or a dipole antenna.

The SIM card microcontroller 106 is configured to store and process useridentification data of users of mobile phone services provided by theoperators, as supported by the RF SIM card 100 and to exchange data withthe main controller 101 a through a standard smart card master/slaveinterface. The SIM card interface module 107 is used for providing anexternal interface between the SIM card 100 and the mobile communicationterminal, which may meet ISO/IEC 7816 specification or other standards.

FIG. 4 is a schematic view of a planar structure of the RF SIM card 100.As shown in FIG. 4, the RF SIM card 100 may include a circuit functionalmodule region 201 and a coupling coil region 202. The circuit functionalmodule region 201 includes hardware circuitry of the main controller 101a, the RF data transceiver module 102, the magnetic signal transmittingmodule 104, the magnetic signal receiving module 105, the SIM cardmicrocontroller 106, and the SIM card interface module 107. The couplingcoil region 202 may be a PCB coil printed around the card body of the RFSIM card 100. Further, the coupling coil 202 may be wound in a singlelayer or multi-layers. Based on the number of layers of the PCB of theRF SIM card 100, the number of turns of the coupling coil may be set ina range from 10 to 40 turns, with the outer-most round is approximatelythe outer dimensions of the RF SIM card 100, such as 25 mm by 15 mm.

FIG. 5 illustrates an exemplary implementation where the low-frequencyreceiving channel and transmitting channel of the SIM card 100 share acoupling coil 302 and the low-frequency receiving channel andtransmitting channel are switched by an analog switch 301.

As shown in FIG. 5, the exemplary system includes the main controller101 a, the magnetic signal transmitting module 104, the magnetic signalreceiving module 105, an analog signal switch 301, and the coupling coil302. The main controller 101 a provides a switching control signal,which is a square wave signal with alternating high and low cycles,whose period may be adjusted according to the real applications. Theswitching control signal controls the analog switch 301.

For example, when the switching control signal is high, the analogswitch 301 is controlled to connect the magnetic signal transmittingmodule 104; when the control signal is low, the analog switch 301selects the magnetic signal receiving module 105. Thus, thelow-frequency receiving channel and transmitting channel can share thecoupling coil 302, saving space and product cost. The analog switch 301can be an SPDT or DPDT switch or any appropriate controllable switch.

FIG. 6 illustrates an exemplary application scenario of the RF SIM card.As shown in FIG. 6, the RF SIM card 100 is embodied in a mobilecommunication terminal 401. The mobile communication terminal 401 andcorresponding RF card reader 402 perform communication distance controland data exchange through bi-directional low-frequency channel andbi-directional RF channel between the terminal and the card reader. TheRF card reader 402 then uploads the field data through correspondingwired data link to the backend server 403 for further processing.

FIG. 7 illustrates another example of a low-frequency two-way radiocommunication and subsequent transaction execution based on the RF SIMcard. As shown in FIG. 7, a transaction process is provided in mobilepayment type applications using the RF SIM card. The transaction processmay include the following steps.

Step 501, in order to reduce unnecessary power consumption, the RF SIMcard by default is in a sleep mode in the absence of any transaction.When the mobile communication terminal equipped with the RF SIM cardenters into a low-frequency magnetic field generated by thecorresponding RF card reader, the process goes to Step 502. The sleepmode may refer to a state where the internal circuitry of the RF SIMcard is in a standby mode, a power-down mode, or a low-power mode.

Step 502, the RF SIM card is activated by low-frequency magnetic fieldgenerated by the corresponding RF card reader, and opens thelow-frequency magnetic signal reception channel and selects a receivingmode. The process proceeds to Step 503. The activating may refer to astate where the internal circuitry of the RF SIM card goes to a normaloperation mode, which is also called wake-up.

Step 503, the RF SIM card receives the first low-frequency alternatingmagnetic field signal transmitted by the RF card reader through thelow-frequency magnetic signal reception channel. The first low-frequencyalternating magnetic field carries the ID of the RF card reader and arandom number, etc., for a number of bytes in length. The RF SIM cardanalyzes the low-frequency magnetic field information, and the processproceeds to Step 504.

Step 504, the RF SIM card detects the strength of the firstlow-frequency alternating magnetic field signal, and compares thedetected strength with a first preset threshold value used for distancecontrol to determine whether the detected strength is within a distancerange based on the preset threshold value. If the detected value doesnot meet the requirements of the preset threshold value, it indicatesthat the mobile terminal equipped with the RF SIM card is not within thecommunication distance range required by the RF card reader, and theprocess goes to Step 512.

On the other hand, if the detected value meets the requirements of thepreset threshold value, it indicates that the mobile terminal equippedwith the RF SIM card is within the communication distance range requiredby the RF card reader, and the process proceeds to step 505.

Step 505, the low-frequency RF SIM card opens the low-frequency magneticsignal transmission channel and selects a transmitting mode, ready torespond to the request of the RF card reader through the low-frequencymagnetic signal transmission channel. The process proceeds to Step 506.

Step 506, the RF SIM card uses a certain encoding format, and a certainmodulation format if necessary, to send corresponding low-frequencyresponse data to the RF card reader through the low-frequency magneticsignal transmission channel. The response data is also referred to asthe second low-frequency alternating magnetic field signal. The processproceeds to Step 507 and Step 518, respectively, where the RF channel ofthe RF SIM card performs Step 507, and the low-frequency magnetic signalchannel of the RF SIM card performs Step 518.

The low-frequency response data is generated based on the low-frequencymagnetic field information the RF SIM card receives from the RF cardreader, and the low-frequency response data includes the ID of the RFSIM card, a random number, an RF communication frequency, and an RFcommunication address, etc., for a number of bytes in length.

Step 507, the RF SIM card selects to open the corresponding RF receivingchannel and the frequency of the RF receiving channel and thecommunication address are the same as the RF communication address andfrequency included in the low-frequency response data. The processproceeds to Step 508.

Step 508, the RF SIM card receives RF data from the RF card readerthrough the RF receiving channel in Step 507. If corresponding RF datais received, the process proceeds to Step 509. If corresponding RF datais not received, the process proceeds to Step 515.

Step 509, the SIM card selects to open the corresponding RF datatransmission channel, and the frequency and address of the correspondingRF data transmission channel are determined based on the information inthe RF data received by the RF SIM card in Step 508. The process thenproceeds to Step 510.

Step 510, the RF SIM card enters into the RF data transceiver mode andexchange transaction data with the RF card reader through the process ofthe two-way RF transceiving channel, and the process then proceeds toStep 511.

Step 511, when the transaction between the RF SIM card and the RF cardreader is completed, the RF SIM card goes back to the sleep mode,waiting for a next transaction.

Step 512, within certain time t1, the RF SIM card continues to try toreceive the low-frequency magnetic field information (i.e., the firstmagnetic signal) emitted by the RF card reader, and the process thenproceeds to Step 513.

Step 513, if the RF SIM card receives the low-frequency magnetic fieldinformation emitted by the RF card reader with the time t1 in step 512,the process returns to Step 504. If the RF SIM card does not receive thelow-frequency magnetic field information emitted by the RF card readerwith the time t1 in step 512, the process returns to Step 514.

Step 514, the mobile communication terminal equipped with the RF SIMcard disconnects the connection between the RF SIM card and the RF cardreader, without continuing the transaction, and the RF SIM card returnsto the sleep mode.

Step 515, within a certain time t2, the RF SIM card continues to waitfor receiving the RF data transmitted by the RF card reader over the RFreceiving channel in Step 508, and the process proceeds to Step 516.

Step 516, if the RF SIM card receives the RF data transmitted by the RFcard reader with the time t2 in step 515, the process returns to Step509. If the RF SIM card does not receive the RF data transmitted by theRF card reader within the time t2 in step 515, the process returns toStep 517.

Step 517, the mobile communication terminal equipped with the RF SIMcard disconnects the connection between the RF SIM card and the RF cardreader, without continuing the transaction, and the RF SIM card returnsto the sleep mode.

Step 518, the RF card reader continuously transmitting low-frequencymagnetic field signals containing distance control information (i.e.,the first low-frequency alternating magnetic field signal). The RF SIMcard again switches the low-frequency channel back to the low-frequencymagnetic signal receiving channel, selects the receiving mode to waitfor receiving the low-frequency magnetic field signal. The processproceeds to Step 519.

Step 519, when the RF SIM card performs RF data exchange with the RFcard reader through the RF channel, at the same time, the RF SIM cardcontinuously detects low frequency magnetic information emitted by theRF card reader over the low-frequency magnetic signal receiving channel.The process proceeds to Step 520.

Step 520, the RF SIM card determines whether the low-frequency magneticfield intensity of the detected low-frequency magnetic field signal(i.e., the first low-frequency alternating magnetic field signal) iswithin the range required for distance control. If the firstlow-frequency alternating magnetic field signal strength meets therequirement, indicating that the communication distance between themobile communication terminal equipped with the RF SIM card and the RFcard reader are still within a valid range, the process then proceeds toStep 510. If the first low-frequency alternating magnetic field signalstrength does not meet the requirement, indicating that thecommunication distance between the mobile communication terminalequipped with the RF SIM card and the RF card reader are beyond a validrange, the process then proceeds to Step 521.

Step 521, the mobile communication terminal equipped with the RF SIMcard disconnects the connection between the RF SIM card and the RF cardreader, without continuing the transaction, and the RF SIM card returnsto the sleep mode.

The above method may also be applied by switching the roles of the RFSIM card and the RF card reader, with the RF card reader performsdistance determination by receiving a second low-frequency alternatingmagnetic field signal emitted by the RF SIM card.

Thus, according to the disclosed embodiments, by detecting the one-wayfirst alternating magnetic field signal from the RF SIM card by the cardreader, the communication distance for card transactions can beeffectively controlled. Further, for RF SIM cards with two-waylow-frequency capability, two-way low frequency distance control can berealized by low-frequency magnetic signal receiving and transmissionmodules, the effective communication distance between the mobilecommunication terminal equipped with the RF SIM card and the RF cardreader supporting the RF SIM card can be precisely controlled in alimited and reasonable range, overcoming the concern that thetransaction distance is easily enlarged while using the RF SIM card withthe one-way distance control. The user experience can be enhanced.

Embodiment Two

According to the disclosed embodiment, an RF card (e.g., an RF SIM card)transmits a first low-frequency alternating magnetic field signalthrough the low frequency channel in accordance with presetlow-frequency transmission parameters, and the transmission frequency isfrequency f. The card reader detects the magnetic field signal at eachdistance point and amplifies the signal into an electrical signal (e.g.,a voltage signal or current signal) with constant amplitudecorresponding to the distance. Further, a preconfigured first thresholdvalue is used to determine whether the mobile terminal enters into apredetermined valid card transaction range (also called effectivedistance range, i.e., the range allowing card transactions). Thepreconfigured first threshold value is the same for all mobileterminals, without the need for calibration. When the mobile terminalenters into a valid card transaction range, the card reader obtainsidentification information IDc of the RF card from the low-frequencyalternating magnetic field signal. The card reader and the RF cardgenerate the same first RF communication address and first frequency,and the card reader sends its own identification information IDr to theRF card using the first RF communication address and first frequency.Further, the RF card and the card reader generate the same second RFcommunication address and second frequency based on the identificationinformation IDc of the card reader for exchanging data information usingan RF channel. Thus, the RF card reader and the RF card can be uniquelybond together by combining the low-frequency one-way communication andtwo-way RF communication and, after the binding, two-way high-speedcommunication with large data can be completed via the RF channel. Thus,the data communication distance (i.e., transaction distance) between theterminal having the RF SIM card (e.g., a mobile phone with an RF SIMcard) and the RF card reader can be effectively controlled within apreset range, and no calibration is needed for the terminal. Morespecifically, the following steps are illustrated.

Step a1, the RF card transmits the first low-frequency alternatingmagnetic field signal.

More specifically, the RF card can transmit the first low-frequencyalternating magnetic field signal through a low-frequency channel basedon preset transmission parameters. The first low-frequency alternatingmagnetic field signal can carry identification information of the RFcard. The preset transmission parameters may include the frequency ofthe first low-frequency alternating magnetic field signal, and thefrequency is equal to or less than the maximum operating frequency f0 ofthe low-frequency channel. The identification information may be theidentification code ID.

The lower the low-frequency alternating magnetic field frequency, thesmaller the attenuation difference after penetrating mobile terminals.Accordingly, from the frequency selection system (as shown in FIG. 8),frequencies with sufficiently small difference can be selected toachieve distance control without calibration. Using a standard signalsource, a built-in transmitter coil in each RF card mounted withinvarious typical mobile terminals transmits a low-frequency alternatingmagnetic field signal. The card reader receives the low-frequencyalternating magnetic field signal, adjust the transmission frequencyuntil finding the frequency f0, so that the voltage received by the cardreader (this voltage is the voltage signal with a constant amplitudecorresponding to the distance from amplifying the low frequencyalternating magnetic field signal) causes the difference of the fieldintensity coming out from different terminals and obstacles, having thesame distance to the center point of the transmitter coil plane,substantially within a preset fluctuation range δ_(T). The frequency f0and the frequency band lower than the frequency f0 belong to thefrequency band of the low-frequency channel communication mode, and nocalibration is needed for any terminal at that frequency. If theoperating frequency (i.e., the frequency of the first low-frequencyalternating magnetic field signal) is higher than f0, the system mayneed to be calibrated. In general, the more operating frequency higherthan the f0, the more terminals need to be calibrated, and the morecomplexity of the calibration. The frequency selection may be performedone-time and, once selected, can be used without change.

FIG. 8 is a structural block diagram of a selection system for selectingthe maximum operating frequency f0 of the low-frequency channel. Asshown in FIG. 8, in one embodiment, the selection system forlow-frequency channel maximum operating frequency f0 comprises: atransmission system containing a signal source 601 and various typicalmobile terminal 602 (including transmitter coil 603 and variousobstacles), a receiving system containing low-frequency receiving module604 (including low-frequency receiver coil 605 and low-frequencyreceiving circuit 606), and a signal strength detector 607 (a voltmeter,an oscilloscope, a spectrometer, etc.).

The principle of detecting voltage and distance curve (voltage-distancecurve) includes: the signal source 601 generates a sine wave signal withfixed amplitude and of frequency f, which is transmitted by thetransmitter coil 603 in the mobile terminal 602, and the signal passesthrough or is diffracted through the typical mobile terminal andobstacles. The low-frequency receiver module 604 converts the receivedlow-frequency signal and passes the signal to the signal strengthdetector 607 through a dedicated signal line, and the signal strengthdetector 607 detects the received voltage. By changing the distance ofthe mobile terminal, the low-frequency receiving module receivescorresponding signals from the mobile terminal and obstacles, and thecurve of the detection voltage changes with the distance can beobtained, i.e., the voltage-distance curve. The mobile terminal andobstacles can be changed to obtain curves of different mobile terminals,and the frequency f can also be changed to obtain different curves.

When the frequency of the low-frequency magnetic field signal is lessthan or equal to the frequency f0, the different mobile terminals withthe radio card are within an effective communication distance range, andno calibration is needed. The frequency f0 can be determined by thefollowing steps.

Step 101, determining the system distance control target (Din, Dv) basedon the first low-frequency alternating magnetic field signal, where Dinmeans that all terminals (with the RF card) within the range of 0-Dinare ensured for card transaction, and Dv denotes the distancefluctuation range. If the distance is within Din˜(Din+Dv), cardtransactions are allowed and, if the distance is greater than Din+Dv,card transactions are not allowed.

For example, (5 cm, 5 cm) means that all terminals within 5 cm areensured for card transactions, all terminals within 5 cm˜10 cm areallowed card transactions, and all terminals beyond 10 cm are notallowed card transactions. The distance control target may be determinedby specific applications, and (0˜Din+Dv) is called distance controlrange.

Step 102, determining the fluctuation range δ_(R) of the detectedvoltage caused by the card reader itself.

That is, the fluctuation of the induced voltage caused by thefluctuation on the parameters of the card reader low-frequency receivercircuit. The parameters include the receiving antenna deviation,amplifier gain deviation, filter deviation, comparator or AD deviation,temperature deviation, and noise, etc. The fluctuation range δ_(R) maybe controlled by the card reader design and production processes.Because the working frequency of the low-frequency receiver circuit issubstantially low, the fluctuation range δ_(R) can be controlleddesiredly, such as less than 4 dB.

Step 103, determining the fluctuation range δ_(C) of the detectedvoltage caused by the RF card.

That is, the fluctuation of the low-frequency transmitting fieldintensity caused by the fluctuation on the parameters of the RF cardlow-frequency transmission circuit. The parameters include the drivercircuit parameter deviation, transmitter coil deviation, temperaturedeviation, and noise, etc. The fluctuation range δ_(C) may be controlledby the RF card design and production processes. Because the operatingfrequency of the RF card low-frequency transmission circuit issubstantially low, the fluctuation range δ_(C) can be controlleddesiredly, such as less than 4 dB.

Step 104, determining the voltage-distance curve of various typicalterminals and obstacles at the frequency f.

Before the Step 104, certain preparation work needs to be performed,i.e., selecting typical terminals and typical obstacles. Selection oftypical terminals is primarily based on the amount of metal orconductive structures of a terminal. The more metal included, the morethe attenuation. For example, typical terminals can be selected asterminals with plastic housing, with metal housing, with a thick metalshell, with a thin metal shell, with a large size, and with a smallsize, etc. The number of typical terminals is not limited, as long asthe selected typical terminals substantially cover the attenuationcharacteristics of the low-frequency alternating magnetic field signalcaused by terminals.

To avoid extraordinary deviation from any particular mobile terminal,the type of the mobile terminal may need to be confirmed inapplications. Each type of mobile terminal for transaction applicationsmay be tested to determine the attenuation characteristics of the typeof mobile terminal. Typical obstacles may be selected as standard shapeswith different materials, such as plastic, aluminum, copper, iron,stainless steel, and other common materials used in mobile terminals.The typical obstacles are placed between the card reader and the mobileterminal as an equivalent obstacle of mobile terminal attenuationcharacteristics for measuring attenuation effect. The typical terminaland obstacle may represent equivalent attenuation characteristics of acorresponding mobile terminal with respect to signal attenuationeffects.

Step 105, based on the distance control target (Din, Dv), determiningfluctuation range δ_(A) of the detection voltage by the card reader. Therange δ_(A) equals to the difference between the voltage correspondingto the point Din on the voltage-distance curve with average fieldintensity attenuation curve slope and obtained from the voltage-distancecurves of various typical terminals and obstacles and the voltagecorresponding to the point (Din+Dv).

FIG. 9 illustrates the total received detection voltage fluctuationrange δ_(A) determined by the distance control target (Din, Dv). Asshown in FIG. 9, the point Din corresponds to voltage value V1, and thepoint (Din+Dv) corresponds to the voltage value V2, and δ_(A)=V1−V2.

Step 106, determining the fluctuation range δ_(T) of the card readerdetection voltage caused by the mobile terminal. The parameter δ_(T)represents the fluctuation range of the card reader detection voltagecaused by the attenuation characteristics of the terminal,δ_(T)=δ_(A)−δ_(R)−δ_(C).

FIG. 10 illustrates a voltage-distance curves and fluctuation range δ ofa typical terminal and obstacle. As shown in FIG. 10, thevoltage-distance curve corresponding to the maximum attenuation terminaland obstacle is called the maximum attenuation curve, andvoltage-distance curve corresponding to the minimum attenuation terminaland obstacle is called the minimum attenuation curve. The areasurrounded by the maximum attenuation curve and the minimum attenuationcurve is called the voltage-distance curve distribution area of thetypical terminal and obstacle. Provided that the voltage correspondingto any D on the minimum attenuation curve is V3, and the voltagecorresponding to any D on the maximum attenuation curve is V4, thenδ=V3−V4.

Step 107, calculating the maximum field intensity difference δ (alsocalled the fluctuation range) emitted from various distances with thedistance control range of various typical terminals and obstacles. If δis greater than δ_(T), the frequency f is decreases and the method goesto Step 104. If δ is less than δ_(T), the frequency f is increased andthe method goes to Step 104. Further, if δ is equal to δ_(T), thecurrent frequency f is equal to the frequency f0.

Thus, in the case of limited distance control target, the maximumoperating frequency f0 of the system's low-frequency channel can bedetermined. The low-frequency channel may use a modulation mode, or mayuse another mode to directly transmit baseband signal mode. Inoperation, the maximum main frequency component of the system is nogreater than the frequency f0, and the distance control does not need tobe calibrated.

In one embodiment, the communication frequency f of the low-frequencychannel may be selected in such way as to avoid the environmental noise,especially the audio noise.

Further, the transmission parameters of the low-frequency alternatingmagnetic field signal can also include modulation mode, coding mode, andtransmission magnetic flux density (or magnetic induction intensity) Bc.The transmission parameters are selected to ensure that the signaldetected and amplified by the card reader from the first low-frequencyalternating magnetic field signal transmitted by the RF card at variousdistances is a voltage signal with constant amplitude and correspondingto the distance. FIG. 11 illustrates detection voltage signal detectedby the card reader for directly-transmitted baseband signal withoutmodulation and the voltage waveform diagram of the detected voltagesignal for a sine-wave FSK modulation. In FIG. 11, 11(a) is the voltagewaveform diagram of the received voltage signal for directly-transmittedbaseband signal without modulation, and 11(b) a voltage waveform diagramof the received voltage signal for a sine-wave FSK modulation. As shownin FIG. 11, the detection voltage signal is a variable voltage signalcontaining demodulation information. The signal may be an AC voltagesignal without any DC component, or may be a voltage signal having a DCcomponent. The constant amplitude means that the maximum amplitude ofthe AC component in different transmission symbols keeps constant.

The modulation mode, coding mode, and transmission magnetic flux densityBc of the transmission parameters of the first low-frequency alternatingmagnetic field signal may be selected through the following Step a11 toStep a13.

Step a11, selecting any coding mode without an average DC component,such as Manchester, Differential Manchester, NRZ, etc.

Step a12, selecting no modulation or a carrier modulation mode withoutamplitude change. The carrier modulation mode can use any modulationmethod without amplitude change. For example, the carrier wave may be asine wave carrier, a pulse carrier, or a triangle wave carrier, etc. Themodulation may be on-off keying (OOK), phase shift keying or frequencyshift keying (FSK), etc. In the no-modulation mode, the encoded basebandsignal is directly driven by the driver circuit and transmitted by thetransmitter coil.

Step a13, selecting the transmission magnetic flux density Bc of thelow-frequency channel. Specifically, under a selected operatingfrequency that is less than f0, a selected modulation scheme and aselected coding mode, first selecting the magnetic detection and theamplification gain that are easy to achieve by the card reader, thendetecting inherent noise voltage amplitude Vn of the detection voltageof the card reader when the RF card is not sending the firstlow-frequency alternating magnetic field signal. Further, detecting thedetection voltage Vr of the card reader when the RF card is sending thefirst low-frequency alternating magnetic field signal using the selectedmodulation and coding. The transmission magnetic flux density Bc isselected such that Vr/Vn>SNR, where SNR is the signal-noise-ratio of thelow-frequency signal of the card reader. In general SNR value may beselected as large as possible, as not to cause the transmission power ofRF communication device to be too high. For example, the SNR may beselected as SNR=10. After the SNR is determined, Bc is also determinedas described above.

Step b1, the card reader detects the first low-frequency alternatingmagnetic field signal.

Specifically, the RF card reader receives and detects the firstlow-frequency alternating magnetic field signal sent by the RF card ateach distance through the low-frequency channel, and amplifies the firstlow-frequency alternating magnetic field signal into an electricalsignal (a voltage signal or a current signal) with constant amplitudeand corresponding to the distance. Further, based on a first presetthreshold value, the card reader determines whether the terminal withthe RF card enters into the effective card transaction range. When theterminal with the RF card enters the effective card transaction range,the card reader obtains the identification information IDc of the RFcard carried in the first low-frequency alternating magnetic fieldsignal. The first preset threshold value may be set the same for allterminals with the RF card.

If the first low-frequency alternating magnetic field signal isamplified into a voltage signal with constant amplitude andcorresponding to the distance, the corresponding first preset thresholdis the voltage threshold. The preset voltage threshold Vt can be setthrough the following Step 201 to Step 203.

Step 201, under the selected transmission parameters, measuring thevoltage-distance curve obtained by the card reader from various typicalterminals and obstacles. The transmission parameters include frequencyof the low-frequency alternating magnetic field signal, modulation mode,coding mode, and transmission magnetic flux density Bc, etc.

Step 202, obtaining a reference voltage-distance curve, the referencevoltage-distance curve is the middle value of the curves of the typicalterminals and obstacles, the voltage magnitude from the upper boundaryand the lower boundary of the curves the typical terminals and obstaclesis δ_(T)/2, as shown in FIG. 10.

Step 203, selecting the threshold value Vt of the detection voltage ofthe card reader, as shown in FIG. 12. The voltage value at the point(Din+Dv/2) on the reference voltage-distance curve is Vt.

If the voltage signal corresponding to the received low-frequencyalternating magnetic field signal is greater than or equal to the presetthreshold value Vt, it can be determined that terminal with the RF cardenters the effective card transaction range.

Step c1, the card reader sends its own identification information IDrthrough the RF channel.

Specifically, if the electrical signal corresponding to the receivedfirst low-frequency alternating magnetic field signal is greater than orequal to the preset first threshold value, the terminal with the RF cardenters the effective card transaction range, the card reader obtains theidentification information IDc of the RF card from the received firstlow-frequency alternating magnetic field signal and, based on theidentification information IDc of the RF card, communicate with the RFcard to generate the same first RF communication address and firstfrequency. Further, the card reader sends its own identificationinformation IDr to the RF card through the first RF communicationaddress and first frequency.

Step d1, the RF card obtains the identification information IDr of thecard reader, and exchange information with the card reader through theRF channel.

Specifically, the RF card obtains the identification information IDr ofthe card reader, the RF card and, based on the identificationinformation IDr of the card reader, communicate with the card reader togenerate the same second RF communication address and second frequency.The RF card and the card reader can subsequently exchange informationusing the second RF communication address and second frequency.

In certain embodiments, after confirming that the RF card enters theeffective card transaction range by detecting the first low-frequencyalternating magnetic field signal, the card reader can conduct cardtransactions with the RF card through the RF channel (or conduct dataexchange). The RF channel address and frequency for the cardtransactions may be fixed address and frequency preconfigured for the RFcard and the card reader and separately stored on the RF card and thecard reader, or may be dynamic address and frequency calculated by theRF card and the card reader using the same algorithm. Other ways forsetting the RF channel address and frequency may also be used. Forexample, the card reader obtains the identification information IDc ofthe RF card from the received first low-frequency alternating magneticfield signal and, based on the identification information IDc of the RFcard, communicate with the RF card to generate the same first RFcommunication address and first frequency, and then start data exchange(or card transactions) using the first RF communication address andfirst frequency, without sending the identification information IDr ofthe card reader itself or generating the second RF communication addressand second frequency for data exchange.

Thus, through the above steps, the card reader and the terminal with theRF card in a communication system can be uniquely bond, thecommunication distance can be effectively controlled within apredetermined range, and the mobile terminal does not need calibration.

Additionally, because the current required for the low-frequencytransmission magnetic field intensity of the low-frequency channel isdrawn from the mobile terminal, the current can be provided by themobile terminal usually is limited to, for example, a maximum of 50 mA,the communication distance of the low-frequency channel will not beexpanded too much even when the transmission parameters of the mobileterminal is tampered, and the effective communication distance can stillbe controlled within about Din˜Din+Dv range.

Further, the frequency of the low-frequency alternating magnetic fieldsignal may be in the low frequency band, very-low frequency band, orultra-low frequency band. For example, the ultra-low frequency band maybe in a range of approximately 300 Hz˜3000 Hz, the very-low frequencyband may be in a range of approximately 3 KHz˜30 KHz, and the lowfrequency band may be in a range of approximately 30 KHz˜300 KHz. Incertain embodiments, the frequency of the low-frequency alternatingmagnetic field signal can be in a range of approximately 300 Hz˜50 KHz,such as 10 KHz, 15 KHz, 20 KHz, 25 KHz or 30 KHz.

Thus, according to the disclosed embodiments, using a one-way detectionof the first low-frequency alternating magnetic field signal sent by theRF card to the card reader, the communication distance for cardtransactions can be effectively controlled, improving the issue ofuncontrollable communication distance problems and increasing thesecurity of card transactions. Thus, using the disclosed communicationmethod, the communication distance (i.e., the transaction distance)between a mobile terminal with an RF card (e.g., a mobile phone with anRF SIM card) and the card reader can be reliably controlled within apredetermined range, without the need to calibrate the terminal.Moreover, using the disclosed communication method, the insecure factorssuch as the card transaction distance exceeding the preconfigured cardtransaction distance due to maliciously tampering of the card reader canbe avoided, enhancing the security of mobile payments and othertransactions.

FIG. 13 is a block diagram of an overall structure of a communicationsystem according to disclosed embodiments. As shown in FIG. 13, in thisembodiment, the communication system 70 includes a card reader 710 andan RF card 720. The card reader 710 and RF card 720 control thecommunication distance through the first low-frequency alternatingmagnetic field signal, and exchanges information through the RF channel.

The card reader 710 includes a magnetic signal receiver 711 and a firstRF communication unit 712. The magnetic signal receiver 711 isconfigured to receive and demodulate the first low-frequency alternatingmagnetic field signal, and the first radio communication unit 712 isconfigured to exchange information with a second RF communication unit722. The RF card 720 includes a magnetic signal transmitter 721 and thesecond RF communication unit 722. The magnetic signal transmitter 721 isconfigured to generate and transmit the first low-frequency alternatingmagnetic field signal, and the second RF communication unit 722 isconfigured to exchange information with the first RF communication unit712.

FIG. 14 is a specific configuration of the magnetic signal receiver 711and the magnetic signal transmitter 721. As shown in FIG. 14, themagnetic signal receiver 711 may comprise a determination unit 7111. Thedetermination unit 7111 is configured to determine whether the cardreader enters the preset effective card transaction range based on thefirst low-frequency alternating magnetic field signal detected by thecard reader. Further, as shown in FIG. 14, the magnetic signaltransmitter 721 may include a modulation unit 7211, and the modulationunit 7211 is configured to add the identification information of the RFcard 720 into the first low-frequency alternating magnetic field signal.

Of course, the magnetic signal receiver may further include a magneticsignal receiving unit (not shown), and the magnetic signal transmittermay further include a signal transmitting unit (not shown) and the like,the detailed descriptions of which are omitted herein.

It should be noted that, those skilled in the art can understand thatthe multiple modules or units may be combined into one module or unit,and one module or unit can be further divided into multiple sub-modulesor sub-units.

FIG. 15 illustrates a detailed structural diagram of a communicationsystem according to disclosed embodiments. As shown in FIG. 15, in thisembodiment, the communication system includes a card reader 001 and anRF card 002.

The card reader 001 includes a low-frequency magnetic induction circuit015, a low-frequency amplifying and filtering circuit 014, a thresholdjudgment and demodulation circuit 013, and a first main processor 012,etc. The low-frequency magnetic induction circuit 015, the low-frequencyamplifying and filtering circuit 014, the threshold judgment anddemodulation circuit 013 and first main processor 012 may besequentially connected in series. The card reader 001 may also includean RF transceiver circuit 017 and an RF antenna 016. The RF antenna 016,the RF transceiver circuit 017, and the first main processor 012 mayalso be sequentially connected in series.

The RF card 002 includes a low-frequency transmitter coil 026, a drivecircuit 025, an encoding circuit 023, and a second main processor 022.The low-frequency transmitter coil 026, the driver circuit 025, thesecond encoding circuit 023, and the main processor 022 may besequentially connected in series. The RF card 002 may also include an RFtransceiver circuit also 027 and an RF antenna 028. The RF antenna 028,the RF transceiver circuit 027, and the second main processor 022 may besequentially connected in series. There may be a modulation circuit 024provided between the drive circuit 025 and the encoding circuit 023, andthe drive circuit 025, the modulation circuit 024, and the encodingcircuit 023 may be sequentially connected in series.

In certain embodiments, the low-frequency transmitter coil may be a wirecoil or a PCB coil. Further, the low-frequency transmitter coil may havemore than 4 turns. The low-frequency magnetic induction coil circuit canbe a PCB coil, a wire coil, a Hall device or a giant magnetoresistivedevice. In certain embodiments, the low-frequency magnetic inductioncoil circuit in the card reader may use a low-frequency receiver coil,and the low-frequency receiver coil may have 50-500 turns.

In certain embodiments, the maximum width of the sectional areasurrounded by the low-frequency receiver coil is greater than the widthof the cross-sectional area of the RF card. For example, the sectionalarea surrounded by the low-frequency receiver coil may include at leasta circular cross-sectional area with a diameter of 3 cm or a square areaof 3 cm×3 cm.

The implementation of the communication system is illustrated asfollows.

(1), The communication frequency f0 of the low-frequency channel can beselected using previously-describe methods, the details of which are notrepeated herein.

(2), The Process for Distance Control and Connection the RF Card to theCard Reader.

First, the card reader is in a low-frequency receiving state. The RFcard can self-wakeup the low-frequency transmitter function at a presetfixed time period. When the RF card is in the wakeup state, the RF cardtransmits the first low-frequency alternating magnetic field signal at afrequency no higher than the selected frequency f0 using preconfiguredtransmission parameters. The first low-frequency alternating magneticfield signal carries a data frame based on modulated signal or directbaseband signal. The data frame contains a unique identifier IDc of theRF card (of course also other identification information that canuniquely identify the RF card). When the mobile terminal with the RFcard is placed around the card reader, the first low-frequencyalternating magnetic field signal penetrates the typical obstacles inthe terminal and reaches the low-frequency detection end of the cardreader. The card reader detects and amplifies the first low-frequencyalternating magnetic field signal transmitted by the RF card at eachdistance point into a voltage signal of constant amplitude andcorresponding to the distance point.

When the voltage value is lower than the preset threshold value Vt inthe card reader, it indicates that the terminal does not enter into avalid card transaction range, and card transactions are not allowed.When the voltage amplitude is higher than the preset voltage thresholdVt of the card reader, it indicates that the terminal enters into thevalid card transaction range, the card reader parses the information inthe first low-frequency alternating magnetic field signal, obtains theidentifier IDc of the RF card, and generates a first RF communicationaddress and a first frequency based on the IDc information. The cardreader then transmits its own identification information IDr using thefirst RF communication address and the first frequency.

The RF card obtains the identification information IDr of the cardreader, and generates a second RF communication address and a secondfrequency based on the identification information IDr. The card readerand the RF card of the communication system can complete cardtransactions using the second RF communication address and the secondfrequency. Further, when a card transaction is initiated, the RF card isno longer in the self-wakeup state. Instead, the RF card continuouslytransmits the low-frequency magnetic field signal to ensure that themobile terminal with the RF card and the card reader are always withinthe valid card transaction range. Thus, the RF card and the card readercan be uniquely bond, after which the communication process for dataexchange using the RF channel is less likely to generate errors. Thatis, after the RF card is successfully bond with or connected to the cardreader, the distance control process is completed, and a subsequent cardtransaction can be carried out on the RF channel until the end of thetransaction.

(3), The Transaction Process.

The RF card and the card reader establish the unique and reliablecommunication link through the RF channel. Based on the communicationlink, the two sides can complete the authentication required by thetransaction and other processes required by the transaction. All ofthese processes can be accomplished by a fast RF channel. Because theabove described process can ensure that the connection can only be madewithin a predetermined distance range, the entire transaction processcan also be communication limited within the predetermined distancerange.

As shown in FIG. 15, the communication system consists of two parts: thecard reader 001 and the RF card 002. The RF card 002 is placed inside amobile terminal and interacts with the mobile terminal through terminalcommunication interfaces.

Card reader 001 may comprise the following modules: a first mainprocessor 012, responsible for the card reader low frequency and highfrequency control and processing other protocols, the first mainprocessor 012 can connect to the external communication interface viathe interface circuit 011 or directly; a low-frequency magneticinduction circuit 015 comprising a PCB coil, a wire coil, a giantmagnetoresistive device, a Hall device, or other circuit elementscapable of sensing magnetic field changes, responsible for inducing andconverting the first low-frequency alternating magnetic field signal 003into a first electrical signal; a low-frequency amplifier and filtercircuit 014 responsible for amplifying the electrical signal detected bythe low-frequency magnetic induction circuit and filtering out the noisecomponent; a threshold judgment and demodulation circuit 013 responsiblefor determining the value of the low-frequency electrical signal withthe noise component filtered out and comparing the value with the presetthreshold value Vt. If the value exceeds the preset threshold value Vt,it indicates the RF card enters into a card transaction range. The cardreader demodulates the electrical signal and obtains a coded signal sentby the encoding circuit 023 of the RF card. The demodulated coded signalis transmitted to the first host processor 102, and the first mainprocessor 022 is responsible for decoding processing. The RF transceivercircuit 017 is responsible for completing RF two-way communication withthe RF transceiver module of the RF card 002 through the RF antenna 016,transmitting and receiving RF signals 004.

The RF card 002 may comprise the following modules: a second mainprocessor 022 responsible for controlling low-frequency and RF modulesand processing other protocols and also responsible for communicatingwith the mobile terminal; a SIM/TF/SD card module 021 being internalSIM/TF/SD card module of the mobile terminal, the module type isdetermined by the specific type of the card; an encoding circuit 023,responsible for encoding the low-frequency frame bit by bit; amodulation circuit 024 responsible for modulating the symbol streamoutputted by the encoding module against a carrier wave to generate amodulated signal to the drive circuit 025 or for directly sending theencoded signal to the drive circuit 025 if no modulation is used; thedrive circuit 025, responsible for driving the low-frequency transmittercoil 026 to generate the first low-frequency alternating magnetic fieldsignal 003; an RF transceiver circuit 027 responsible for completing RFtwo-way communication with the RF transceiver module of the card reader001 through the RF antenna 028, transmitting and receiving RF signals004.

The communication system achieves distance detection and control withoutcalibration by determining the low-frequency communication thresholdfrom the mobile terminal to the card reader. That is, the RF card 002transmits the first low-frequency alternating magnetic field signal 003in accordance with the preset transmission parameters, and the cardreader 001 receives the magnetic field signal and converts it into alow-frequency detection voltage signal, and uses a preset thresholdvalue Vt to determine whether the terminal enters the preset validdistance range. If the terminal enters the valid range, the card reader001 obtains the identification information IDc of the RF card 002included in the low-frequency alternating magnetic field signal andgenerate, together with the RF card 002, a first RF communicationaddress and a first frequency based on the information IDc. Further,based on the first RF communication address and the first frequency, thecard reader 001 sends its own identification information IDr. The RFcard 002 receives the identification information IDr of the card reader001 at the first RF communication address and the first frequencythrough the RF channel and, together with the card reader 001, generatesa second RF communication address and a second frequency. The cardreader 001 and the RF card 002 complete subsequent card transactions atthe second RF communication address and the second frequency. By theone-way low-frequency alternating magnetic field signal detection fromthe RF card 002 to the card reader 001, the communication distancecontrol between the RF card 002 to the card reader 001 can be completed.That is, the RF card 002 passes its identity information IDc to the cardreader 001 through the low-frequency channel, and the card reader 001feedback its own identification information IDr to the RF card 002through the RF channel. Both sides using the same identificationinformation for generating the same RF communication address andfrequency, so as to realize the unique binding between the card reader001 and the RF card 002. After the binding, the RF channel can be usedto accomplish high-speed large data volume bi-directional communicationthrough the RF channel.

The specific workflow of the communication system are illustrates in thefollowings.

(A) First, basic operation parameters of the system are selected,including the RF frequency, low-frequency channel communicationfrequency f, RF card transmission parameters, card reader receivingvoltage threshold Vt, card reader receiving circuitry parameters, etc.

1. Selecting the RF Frequency

The RF communication frequency may be selected above 2400˜2483 MH 2.4GISM band, so as to achieve high-speed communication and good terminalpenetration. Other frequency, such as 433 MHz, 900 MHz, 5 GHz, or thelike, can also be used.

2. Selecting the Low-Frequency Channel Communication Frequency f

The method described above can be used to determine the communicationfrequency f of the system's low-frequency channel. For a typical GSMmobile terminal, to achieve a range of 0˜15 cm distance control, withconsideration on noise interference especially the audio interference,the frequency f may be selected between 20 KHZ and 50 KHz, such as 10KHZ, 15 KHZ, 20 KHZ, 25 KHZ, or 0 KHZ, etc.

3. Selecting the RF Card Transmission Parameters

The transmission parameters include modulation mode, coding scheme andtransmission magnetic induction intensity Bc.

FIG. 16 is a schematic diagram of the low-frequency transmitter part ofthe RF card. As shown in FIG. 16, the low-frequency transmitter portionof the RF card includes a low-frequency transmitter circuit and a mobileterminal equipped with the RF card having a built-in low-frequencytransmitter coil. Referring to FIG. 15, the radio frequency transmittercircuit comprises a driving circuit 025, the modulation circuit 024, andthe encoding circuit 023. The low-frequency modulated signal driven bythe driving circuit 025 is outputted to the low-frequency transmittercoil 026.

The modulation circuit 024 can use the following modulation schemes:

(1) Carrier modulation: the baseband signal generated by the encodingcircuit 023 is modulated by the modulation circuit 024 against thecarrier, and the carrier may be a sine wave, a square wave, or atriangular wave, etc. The modulation can use On-off frequency shiftkeying (OOK), phase shift keying, frequency shift keying (FSK), etc. Themodulated signal is loaded onto the low-frequency transmitter coil 026through the driving circuit 025.

(2) No-carrier direct baseband transmission: the baseband signalgenerated by the encoding circuit 023 is loaded directly onto thelow-frequency transmitter coil 026 through the drive circuit 025.

(3) Other modulations: because the distance control is based on thethreshold, the modulation mode used in general less prefers amplitudemodulation, other modulation schemes that can maintain the detectionvoltage amplitude of the RF card substantially constant can also beused.

Encoding circuit 023 can use the following encoding schemes:

(1) Manchester encoding: 1 bit is encoded as two symbols 01, bit 0 isencoded as 10.

(2) Differential Manchester encoding: two bit symbol sequences, 01 and10, bit 1 is encoded differently from the previous symbol sequence, andbit 0 is encoded the same, or vice versa.

(3) Other encoding schemes: because the distance control is based on thethreshold, the encoding may need to keep the average value of thelow-frequency modulated signal, and the encoded sequence does notcontain a DC component. Any encoding scheme resulting in zero average DCcomponent can be used.

After selecting the modulation and coding schemes, the transmissionmagnetic induction intensity Bc can be determined using the methoddescribed previously. The parameter Bc can be adjusted by adjustingturns, diameter, and/or shape of the coil, and gain parameters of thedriving circuit 205.

4. Selecting Card Reader Receiving Voltage Threshold Vt

The card reader receiving voltage threshold Vt can be selected using themethod described previously.

5. Selecting the Card Reader Low-Frequency Receiving CircuitryParameters

Referring to FIG. 15, the card reader low-frequency magnetic inductioncircuit 015 includes a winding-wire coil, a PCB coil, a Hall device, ora giant magnetoresistance device. Any such device with desiredsensitivity can be selected in the low-frequency magnetic inductioncircuit.

The above parameters may only need to be selected once. After they areselected, no change might be required during operation.

(B) Second, the system operational flow after determining the operationparameters:

Step A100: distance detection and control process. The RF card 002 canself-wakeup the low-frequency transmitter function at a preset fixedtime period. When the RF card is in the wakeup state, the second mainprocessor 002 of the RF card 002 generates a data frame containing aunique identifier IDc of the RF card 002 and sends it to the encodingcircuit 023 to be encoded. The encoded signal is modulated by themodulation circuit 024 and passed to the drive circuit 025 or isdirectly passed to the drive circuit 025 without modulation, themodulated voltage is sent to the low-frequency transmitter coil 026.Based on preconfigured frame format, modulation and coding schemes, anddriving capability, the transmitter coil 027 transmits the firstlow-frequency alternating magnetic field signal 003 at the presetintensity Bc in accordance with the selected frame format andtransmission parameters.

When the mobile terminal with the RF card 002 is placed around the cardreader, the first low-frequency alternating magnetic field signal 003penetrates the terminal and reaches the low-frequency detection end ofthe card reader 001. The low-frequency magnetic induction circuit 015 ofthe card reader 001 detects and amplifies the first low-frequencyalternating magnetic field signal into an electrical signal. Theelectrical signal is amplified and filtered out noise component by thelow-frequency amplifier circuit 014 to generate a low-frequencydetection voltage. The threshold judgment and demodulation circuit 013determines the magnitude of the voltage. When the voltage amplitude isless than the preset threshold value Vt, card transactions are notallowed. When voltage amplitude is greater than or equal to the presetthreshold value Vt, it indicates that the terminal enters into thepredetermined effective communication distance range of the card reader.

The frame format in Step A100 can be defined as follows:

FIG. 17 illustrates a low-frequency data frame transmitted by the RFcard. As shown in FIG. 17, the RF card low-frequency data frame includesthe following.

Preamble: 8 bits, usually FFH, for frame synchronization.

Control field: eight bits, providing information for reading the frame,such as length, data type, etc., reserved bits can used for expansion.

IDc: N bits, the unique identifier of the RF card, specified by thecontrol field, where N is a natural number.

CRC: the checksum for the control field and the IDc, CRC checksum orother format can be used.

The above-described frame format is only an example, any frame formatcontaining the unique identifier of the RF card or the card reader canbe used. The unique identifier can be a random number of sufficientlength, the card reader may also be manually assigned a unique code, orother methods may be used to generate the unique identifier.

The unique identifier of the RF card in Step A100 may be a uniqueidentifier pre-stored in the non-volatile memory (NVM) within the RFcard, may be a random number with sufficient length internally generatedby the RF card.

Step A200: in Step A100, the card reader determines that the detectionvoltage is greater than the preset threshold voltage Vt, which indicatesthat the card reader and the RF card reader enter into a valid cardtransaction distance range. The threshold judgment and demodulationcircuit 013 parses the voltage signal to obtain IDc. The first mainprocessor 012 of the card reader 001 and the second main processor 022of the RF card 002 generate the same RF communication address andfrequency based on the IDc information. Using this RF communicationaddress and frequency, the card reader 001 transmits its ownidentification information IDr to the RF card 002 using the RFtransceiver circuit 017 and through the RF antenna 016. The RF antenna028 and RF transceiver circuit 027 of the RF card 002 receive theidentification information IDr at the same RF communication address andfrequency and pass to second main processor 022. The first mainprocessor 012 and second main processor 022 generate a new RFcommunication address and frequency based on the IDr information. Thesystem initiates card transactions at this new RF communication addressand frequency. Further, when a card transaction is initiated, the RFcard 002 is no longer in the self-wakeup state. Instead, the RF cardcontinuously transmits the low-frequency magnetic field signal to ensurethat the card reader 001 and the RF card 002 are always within the validcard transaction range. Thus, the above method can be used to controlsystem communication distance, and the RF card and the card reader canbe uniquely bond. The communication distance between the card reader 001and the mobile terminal with the RF card 002 can be securely andeffectively controlled without calibration.

The unique identifier IDr of the card reader in Step A200 can bepre-stored in the nonvolatile memory (NVM) of the card reader, or arandom number with a sufficient length internally generated by the cardreader.

Step A300: transaction process. The card reader 001 and the RF card 002establish a reliable and unique communication link through the RFchannel. Based on the link, the two sides can complete theauthentication required by the transaction and other processes requiredby the transaction. All of these processes can be accomplished by a fastRF channel. Because Steps A100˜A200 can ensure that the connection tothe RF card 002 can only be made within a predetermined distance range,the entire transaction process can also be communication limited withinthe predetermined distance range. The transaction process may be a POStransaction process, the details are omitted herein.

The low-frequency signal detection circuit 015 of the card reader 001may comprise a PCB coil, a wire coil, a GMR device, or a Hall device.Other sensing device may also be used, so long as the device is capableof converting the magnetic field into an electrical signal, and withdesired magnetic induction sensitivity.

Thus, the disclosed communication system can use low-frequencyalternating magnetic field to achieve distance detection and control,and to achieve one-way low-frequency communication from the RF card tothe card reader. The RF channel can be used in combination with thelow-frequency one-way communication to achieve reliable and uniquebinding with the terminal, and the RF channel can be used to achievehigh-speed data communication between the card reader and the RF card.Certain characteristics include: (1) the mobile terminal does not needto be modified, only needs to replace the SIM/TF/SD card inside themobile terminal and the reliable two-way distance communication can beachieved; (2) because the current provided by the RF card is limited,the communication distance of the low-frequency signal is limited, whichcan prevent the transmission power of the RF card being tampered orincreased, and the communication distance can be effectively controlledwithin a predetermined range. In addition, the RF transceiver circuit isplaced within the RF card to achieve two-way high-speed communicationwith the RF transceiver circuit with the card reader. Because theantenna of the RF circuit is very small, it can be easily integratedinto the SIM/TF/SD card.

According to the disclosed embodiments, the frequency f is selected tobe less than the frequency f0, no calibration is needed when the systemoperates at the frequency f, and the communication distance can becontrolled safely and effectively. As an extension, frequency f may alsobe selected above the frequency f0, which may cause reduced performance,reduced distance control accuracy, and/or reduced communication successrate. However, such use does not conflict with the disclosed invention,and merely an extension with modified performance.

According to the disclosed embodiments, one-way detection of alow-frequency alternating magnetic field signal from the RF card to thecard reader can be used to effectively control the communicationdistance, improving the problem of uncontrollable communication distanceand improving the security of card transaction communication. Moreover,the insecure factors such as the card transaction distance exceeding thepreconfigured card transaction distance due to maliciously tampering ofthe card reader can be avoided, enhancing the security of mobilepayments and other transactions.

Embodiment Three

According to the disclosed embodiment, an RF card reader withlow-frequency alternating magnetic field transmission and receivingfunctions and RF signal transmission and receiving functions is providedto control the distance of near-field communication between the RF cardreader and the mobile terminal equipped with the RF card. Thelow-frequency alternating magnetic field can penetrate differentterminals with small signal attenuation difference, the low-frequencytransmission power of the mobile terminals is limited, the low-frequencyreceiving signal-noise-ratio (SNR) of the RF SIM card is limited, andthe two-way low-frequency transmission distance is also limited. Thus,the two-way distance control between the RF card reader and the mobileterminal can be realized, and high-frequency RF can effectivelypenetrate the terminal to complete high-speed two-way communication toconduct transactions. Thus, the RF card reader and the RF card can beuniquely bond together by combining the low-frequency two-waycommunication and two-way RF communication and, after the binding,two-way high-speed communication with large data can be completed viathe RF channel. Thus, the data communication distance (i.e., transactiondistance) between the terminal having the RF card (e.g., a mobile phonewith an RF SIM card) and the RF card reader can be effectivelycontrolled within a preset distance range, and no calibration is neededfor the terminals.

FIG. 18 illustrates a block diagram of an overall structure of an RFcard reader according to the disclosed embodiments. As shown in FIG. 18,in this embodiment, the RF card reader comprises a magnetic signaltransceiver and an RF communication unit. The magnetic signaltransceiver is configured to generate, transmit, and receivelow-frequency alternating magnetic field signals. The RF communicationunit is configured to exchange information through RF communication. Ofcourse, the magnetic signal transceiver may further include a magneticsignal transmitter and a magnetic signal receiver.

The RF card reader can include a low-frequency radio transmitter module,a low-frequency receiver module, an RF transceiver module and a firstmain processor. The low-frequency transmitter module, the low-frequencyreceiver module, and the RF transceiver module may be connected to thefirst main processor respectively.

The low-frequency transmitter module, the low-frequency receiver module,and the RF transceiver module may include the following structures. Thelow frequency transmitter module includes a low-frequency transmittercoil, a driver circuit, and an encoding circuit. The low-frequencytransmitter coil, the driver circuit, and the encoding circuit may besequentially connected in series, and the encoding circuit may beconnected to the first main processor. The low-frequency receiver moduleincludes a low-frequency magnetic induction circuit, a low-frequencyamplifier and filter circuit, and a low-frequency demodulation circuit.The low-frequency magnetic induction circuit, the low-frequencyamplifier and filter circuit, and the low-frequency demodulation circuitmay be sequentially connected in series, and the low-frequencydemodulation circuit may be connected to the first main processor. TheRF transceiver module includes an RF antenna and an RF transceivercircuit. The RF antenna and the radio transceiver circuit may beconnected in series, and the RF transceiver circuit is connected to thefirst main processor. Further, a modulation circuit can also be providedbetween the driving circuit and the encoding circuit. The drivingcircuit may also include an adjusting circuit.

Among them, the low-frequency transmitter coil or coils can be wire coilor PCB coil. Preferably, the low-frequency transmitter coil can havemore than 10 turns. More preferably, the low-frequency transmitter coilcan have approximately 50 to 500 turns. In other embodiments, thelow-frequency transmitter coil can be filled with a ferrite core or aniron core. The area enclosed by the low-frequency transmit coil mayinclude at least a circular cross-sectional area with a diameter of 3 cmor a square area of 3 cm×3 cm. Preferably, the cross-sectional areasurrounded by the low-frequency transmitter coil may be greater than 10cm². More preferably, the cross-sectional area surrounded by thelow-frequency transmitter coil may be 20 to 1000 cm².

The magnetic induction device used by the low-frequency magneticinduction circuit may be a wire coil, a PCB coil, a Hall device or agiant magnetoresistive device. Preferably, the magnetic induction deviceused by the low-frequency magnetic induction circuit is a wire coil orPCB coil. The PCB coil or wire coil may have more than 10 turns. Morepreferably, the PCB coil or wire coil can have approximately 50 to 500turns. Preferably, when the magnetic induction device used by thelow-frequency magnetic induction circuit is a wire coil or PCB coil, thearea enclosed by the wire coil or PCB coil includes at least a circularcross-sectional area with a diameter of 3 cm or a square area of 3 cm×3cm. Preferably, the cross-sectional area surrounded by the wire coil orPCB coil is greater than 10 cm². More preferably, the cross-sectionalarea surrounded by the wire coil or PCB coil may be 20 to 1000 cm². Whenthe magnetic induction device used by the low-frequency magneticinduction circuit is a wire coil or PCB coil, the low-frequency magneticinduction circuit and the low-frequency transmitter coil can share thesame coil.

The RF card reader may further include a local magnetic field intensitydetecting device. The local magnetic field intensity detecting devicemay be an independent magnetic field detecting device, or may be thelow-frequency receiver module in the RF card reader itself.

The communication system containing the RF card reader (the systemincludes the RF card reader and a mobile terminal equipped with an RFcard) performs a communication method, including the following Steps a2,Step b2, Step c2, and Step d2, each of which is described in detail asfollows.

Step a2, the RF card reader transmits a first low-frequency alternatingmagnetic field signal through a first low-frequency channel based onpreset first transmission parameters. The first low-frequencyalternating magnetic field signal can carry identification informationof the RF card reader. The first transmission parameters may include thefrequency of the first low-frequency alternating magnetic field signal,and the frequency is equal to or less than the maximum operatingfrequency f0 of the first low-frequency channel.

The identification information may be the identification code ID. Itshould be noted that the frequency of the first low-frequencyalternating magnetic field signal is the frequency corresponding to 3 dBbandwidth upper frequency cut-off point of the low-frequency alternatingmagnetic field signal.

The lower the low-frequency alternating magnetic field frequency, thesmaller the attenuation difference after penetrating mobile terminals.Accordingly, from the frequency selection system (as shown in FIG. 19),frequencies with sufficiently small difference can be selected toachieve distance control without calibration. Using a standard signalsource, a standard magnetic transmitter coil transmits a low-frequencyalternating magnetic field signal. The RF card inside the typicalterminal and obstacle receives the low-frequency alternating magneticfield signal, adjust the transmission frequency until finding thefrequency f0, so that the voltage received by the RF card (this voltageis the voltage signal with a constant amplitude corresponding to thedistance from amplifying the low frequency alternating magnetic fieldsignal) causes the difference of the field intensity coming out fromdifferent terminals and obstacles, having the same distance to thecenter point of the transmitter coil plane, substantially within apreset fluctuation range δ_(T). The frequency f0 and the frequency bandlower than the frequency f0 belong to the frequency band of the firstlow-frequency channel communication mode, and no calibration is neededfor any terminal at that system. If the operating frequency (i.e., thefrequency of the first low-frequency alternating magnetic field signal)is higher than f0, the system may need to be calibrated. In general, themore operating frequency higher than the f0, the more terminals need tobe calibrated, and the more complexity of the calibration. The frequencyselection may be performed one-time and, once selected, can be usedwithout change.

FIG. 19 is a structural block diagram of a selection system forselecting the maximum operating frequency f0 of the first low-frequencychannel. As shown in FIG. 19, in one embodiment, the selection systemfor the first low-frequency channel maximum operating frequency f0comprises: a transmission system containing a signal source 505 and alow-frequency magnetic field transmitter coil 504, a receiving systemcontaining a typical mobile terminal 501 and obstacles, and a signalstrength detector 503 (a voltmeter, an oscilloscope, a spectrometer,etc.). A low-frequency receiver module 502 is disposed inside the mobileterminal 501. The signal source 505 may produce a variety of precisefrequency, waveform and amplitude signals. The principle of selectingthe frequency includes: the signal source 505 generates a sine wavesignal with fixed amplitude and of frequency f, which is transmitted bythe transmitter coil 504. The low-frequency receiver module 502 isdisposed inside the selected typical mobile terminal 501 or obstacle,and passes the received low-frequency signal to the signal strengthdetector 503 via a dedicated signal line, and the signal strengthdetector 503 measures the received voltage. By changing the distance ofthe mobile terminal, the curve of the detection voltage changes with thedistance can be obtained, i.e., the voltage-distance curves for themobile terminal or obstacle at the frequency f. The mobile terminal andobstacles can be changed to obtain curves of different mobile terminals,and the frequency f can also be changed to obtain different curves.

Further, in Step a2, the maximum operating frequency f0 of the system'sfirst low-frequency channel can be determined by the following steps.

Step 201, determining the system distance control target (Din, Dv) basedon the first low-frequency alternating magnetic field signal, where Dinmeans that all terminals (with the RF card) within the range of 0-Dinare ensured for card transaction, and Dv denotes the distancefluctuation range. If the distance is within Din˜(Din+Dv), cardtransactions are allowed and, if the distance is greater than Din+Dv,card transactions are not allowed.

For example, (5 cm, 5 cm) means that all terminals within 5 cm areensured for card transactions, all terminals within 5 cm˜10 cm areallowed card transactions, and all terminals beyond 10 cm are notallowed card transactions. The distance control target may be determinedby specific applications, and (0˜Din+Dv) is called distance controlrange.

Step 202, determining the fluctuation range δ_(R) of the detectionvoltage in the RF card that is caused by the RF card reader.

That is, the fluctuation of the induced voltage caused by thefluctuation on the parameters of the RF card reader low-frequencytransmitter circuit. The parameters include transmission drive voltagefluctuation, coil parameter fluctuations, temperature impact, and so on.The fluctuation range δ_(R) may be controlled by the card reader designand production processes. Because the working frequency of thelow-frequency transmitter circuit is substantially low, the fluctuationrange δ_(R) can be controlled desiredly, such as less than 4 dB.

Step 203, determining the fluctuation range δ_(C) of the detectionvoltage caused by the RF card itself.

That is, the fluctuation of the final detection voltage output caused bythe fluctuation on the parameters of the RF card low-frequency receivercircuit. The parameters include the receiving antenna deviation,amplifier gain deviation, filter deviation, comparator or AD deviation,temperature deviation, and noise, etc. The fluctuation range δ_(C) maybe controlled by the RF card design and production processes. Becausethe operating frequency of the RF card low-frequency transmissioncircuit is substantially low, the fluctuation range δ_(C) can becontrolled desiredly, such as less than 4 dB.

Step 204, determining the voltage-distance curve of various typicalterminals and obstacles at the frequency f.

The frequency f may be in the low frequency band, very-low frequencyband, or ultra-low frequency band. For example, the ultra-low frequencyband may be in a range of approximately 300 Hz˜3000 Hz, the very-lowfrequency band may be in a range of approximately 3 KHz˜30 KHz, and thelow frequency band may be in a range of approximately 30 KHz˜300 KHz.

Before the Step 204, certain preparation work needs to be performed,i.e., selecting typical terminals and typical obstacles. Selection oftypical terminals is primarily based on the amount of metal orconductive structures of a terminal. The more metal included, the morethe attenuation. For example, typical terminals can be selected asterminals with plastic housing, with metal housing, with a thick metalshell, with a thin metal shell, with a large size, and with a smallsize, etc. The number of typical terminals is not limited, as long asthe selected typical terminals substantially cover the attenuationcharacteristics of the low-frequency alternating magnetic field signalcaused by terminals.

To avoid extraordinary deviation from any particular mobile terminal,the type of the mobile terminal may need to be confirmed inapplications. Each type of mobile terminal for transaction applicationsmay be tested to determine the attenuation characteristics of the typeof mobile terminal. Typical obstacles may be selected as standard shapeswith different materials, such as plastic, aluminum, copper, iron,stainless steel, and other common materials used in mobile terminals.The typical obstacles are placed between the card reader and the mobileterminal as an equivalent obstacle of mobile terminal attenuationcharacteristics for measuring attenuation effect.

Step 205, based on the distance control target (Din, Dv), determiningfluctuation range δ_(A) of the detection voltage by the RF card. Therange δ_(A) equals to the difference between the voltage correspondingto the point Din on the voltage-distance curve with average fieldintensity attenuation curve slope and obtained from the voltage-distancecurves of various typical terminals and obstacles and the voltagecorresponding to the point (Din+Dv).

FIG. 20 illustrates the total received detection voltage fluctuationrange δ_(A) determined by the distance control target (Din, Dv). Asshown in FIG. 20, the point Din corresponds to voltage value V1, and thepoint (Din+Dv) corresponds to the voltage value V2, and δ_(A)=V1−V2.

Step 206, determining the fluctuation range δ_(T) of the RF carddetection voltage caused by the mobile terminal. The parameter δ_(T)represents the fluctuation range of the RF card detection voltage causedby the attenuation characteristics of the terminal,δ_(T)=δ_(A)−δ_(R)−δ_(C).

FIG. 21 illustrates a voltage-distance curves and fluctuation range δ ofa typical terminal and obstacle. As shown in FIG. 21, thevoltage-distance curve corresponding to the maximum attenuation terminaland obstacle is called the maximum attenuation curve, andvoltage-distance curve corresponding to the minimum attenuation terminaland obstacle is called the minimum attenuation curve. The areasurrounded by the maximum attenuation curve and the minimum attenuationcurve is called the voltage-distance curve distribution area of thetypical terminal and obstacle. Provided that the voltage correspondingto any D on the minimum attenuation curve is V3, and the voltagecorresponding to any D on the maximum attenuation curve is V4, thenδ=V3−V4.

Step 207, calculating the maximum field intensity difference δ (alsocalled the fluctuation range) at various distances with the distancecontrol range of various typical terminals and obstacles. If δ isgreater than δ_(T), the frequency f is decreased and the method goes toStep 204. If δ is less than δ_(T), the frequency f is increased and themethod goes to Step 204. Further, if δ is equal to δ_(T), the currentfrequency f is equal to the frequency f0.

Thus, in the case of limited distance control target, the maximumoperating frequency f0 of the system's first low-frequency channel canbe determined. The first low-frequency channel may use a modulationmode, or may use another mode to directly transmit baseband signal mode.In operation, the maximum main frequency component of the system is nogreater than the frequency f0, and the distance control does not need tobe calibrated.

An example is used to illustrate the process of determining frequencyf0. FIG. 22 shows 5 voltage-distance curves of 5 typical mobileterminals at frequency f of 3.3 KHz. As shown in FIG. 22, the systemdistance control target is (5 cm, 5 cm), the voltage fluctuation rangeof the system range at range 0˜10 cm is about 40 dB, and the fluctuationof the detection voltage in the RF card caused by the RF card reader andthe RF card is both 4 dB, i.e., δ_(R)=δ_(C)=4 dB, δ_(A)=20 dB,δ_(T)=δ_(A)−δ_(R)−δ_(C)=12 dB. Assuming the 5 terminals can be used torepresent all terminals used in the system, the maximum fluctuation ateach distance of the curves is approximately 12 dB. Thus, the maximumfrequency f0 of the system's first low-frequency channel may bedetermined as f0=3.3 KHz.

In Step a2, the first transmission parameters can also includemodulation mode, coding mode, and transmission magnetic flux density Br.The first transmission parameters are selected to ensure that the signaldetected and amplified by the RF card from the first low-frequencyalternating magnetic field signal transmitted by the RF card reader atvarious distances is a voltage signal with constant amplitude andcorresponding to the distance. FIG. 23 illustrates detection voltagesignal detected by the RF card for directly-transmitted baseband signalwithout modulation and the voltage waveform diagram of the detectedvoltage signal for a sine-wave FSK modulation. In FIG. 23, 23(a) is thevoltage waveform diagram of the received voltage signal fordirectly-transmitted baseband signal without modulation, and 23(b) avoltage waveform diagram of the received voltage signal for a sine-waveFSK modulation. As shown in FIG. 23, the detection voltage signal is avariable voltage signal containing demodulation information. The signalmay be an AC voltage signal without any DC component, or may be avoltage signal having a DC component. The constant amplitude means thatthe maximum amplitude of the AC component in different transmissionsymbols keeps constant

The modulation mode, coding mode, and transmission magnetic flux densityBr of the first transmission parameters may be selected through thefollowing Step a21 to Step a23.

Step a21, selecting any coding mode without an average DC component,such as Manchester, Differential Manchester, NRZ, etc.

Step a22, selecting no modulation or a carrier modulation mode withoutamplitude change. The carrier modulation mode can use any modulationmethod without amplitude change. For example, the carrier wave may be asine wave carrier, a pulse carrier, or a triangle wave carrier, etc. Themodulation may be on-off keying (OOK), phase shift keying or frequencyshift keying (FSK), etc. In the no-modulation mode, the encoded basebandsignal is directly driven by the driver circuit and transmitted by thetransmitter coil.

Step a23, selecting the transmission magnetic flux density Br.Specifically, under a selected operating frequency that is less than f0,a selected modulation scheme and a selected coding mode, first selectingthe typical mobile terminal and the magnetic detection and theamplification gain that are easy to achieve by the RF card inside themobile terminal, then placing the mobile terminal with RF card at thefarthest distance control target, i.e., distance Din+Dv, from the RFcard reader. If the RF card uses magnetic induction circuit fordetecting magnetic field intensity, such as a Hall device or a giantmagnetoresistive device to receive the signal, the RF card readertransmits magnetic field signal having constant magnetic flux density(i.e., differential amplitude). Then, detecting inherent noise voltageamplitude Vn of the detection voltage of the RF card when the RF cardreader is not sending the low-frequency alternating magnetic fieldsignal. Further, detecting the detection voltage Vc of the RF card whenthe RF card reader is sending the low-frequency alternating magneticfield signal using the selected modulation and coding scheme. Thus, thetransmission amplitude value Bgate or differential amplitude valueB_RATEgate can be chosen, such that Vc/Vn>SNR, SNR is theSignal-to-noise-ratio of the RF card. In general SNR value may beselected as large as possible, as not to cause the transmission power ofRF card reader to be too high. For example, the SNR may be selected asSNR=10. After the SNR is determined, Br is also determined as describedabove. According to the type of the magnetic induction circuit in thesystem, there can be two types of Br parameter values, the magnetic fluxdensity threshold Bgate for the Hall device or the giantmagnetoresistance device, and magnetic flux density change ratethreshold B_RATEgate for a coil receiver system.

Step b2, the RF card receives and detects the low-frequency alternatingmagnetic field signal sent by the RF card reader at each distancethrough the first low-frequency channel, and amplifies the low-frequencyalternating magnetic field signal into a voltage signal corresponding tothe distance and with constant amplitude. Further, based on a presetvoltage threshold value Vt, it can be determined whether the terminalwith the RF card enters into the effective card transaction range. Thevoltage threshold value Vt may be set the same for all terminals withthe RF card.

In Step b2, the preset voltage threshold Vt can be set through thefollowing Step 301 to Step 303.

Step 301, under the selected transmission parameters, measuring thevoltage-distance curve obtained by the card reader from various typicalterminals and obstacles. The transmission parameters include frequencyof the low-frequency alternating magnetic field signal, modulation mode,coding mode, and transmission magnetic flux density Br, etc.

Step 302, obtaining a reference voltage-distance curve, the referencevoltage-distance curve is the middle value of the curves of the typicalterminals and obstacles, the voltage magnitude from the upper boundaryand the lower boundary of the curves the typical terminals and obstaclesis δ_(T)/2.

Step 303, selecting the threshold value Vt of the detection voltage ofthe RF card: the voltage value at the point (Din+Dv/2) on the referencevoltage-distance curve is Vt.

Step c2, if the voltage signal corresponding to the receivedlow-frequency alternating magnetic field signal is greater than or equalto the preset voltage threshold Vt, the terminal with the RF card entersthe effective card transaction range, the RF card obtains theidentification information of the RF card reader from the receivedlow-frequency alternating magnetic field signal and, based on the secondtransmission parameters, transmits second low-frequency alternatingmagnetic field signal through the second low-frequency channel. Thesecond low-frequency alternating magnetic field signal carries theidentification information of the RF card reader obtained by the RFcard, and the identification information of the RF card itself. Thesecond transmission parameters include the frequency of the secondlow-frequency alternating magnetic field signal. This frequency is equalto or less than the maximum operating frequency f0′ of the system'ssecond low-frequency channel, and f0′ is the maximum operating frequencysatisfying the target communication distance of Din˜Din+Dv′.

In Step c2, the maximum operating frequency f0′ of the communicationsystem's second low-frequency channel can be determined similarly to thefrequency f0. The difference is that the target communication distancerange of the second low-frequency channel is Din˜Din+Dv′. Further, toensure that the communication in the second low-frequency channel can besuccessfully completed at the communication distance of the firstlow-frequency channel, the communication distance fluctuation Dv of thefirst low-frequency channel and the communication distance fluctuationDv′ of the second low-frequency channel have a relationship of Dv<Dv′,detailed descriptions are omitted herein.

Before, Step c2, it needs to determine the corresponding relationshipbetween the induction voltage corresponding to the low-frequencyalternating magnetic field signal, transmitted by the mobile terminalwith the RF card and detected by the RF card reader, and the distance.

Before selecting the communication frequency f′ of the secondlow-frequency channel, it needs to determine that, under the secondlow-frequency channel communication mode, the change patterns of thevoltage-distance curves of all the typical terminal and obstaclesdetected by the RF card reader, and the change patterns of voltage withrespect to change of the frequency.

FIG. 24 is a block diagram of a system for detecting thevoltage-distance curves under the second low-frequency channelcommunication mode. As shown in FIG. 24, the selection system comprises:a transmission system containing a signal source 801 and various typicalmobile terminals 802 (including transmitter coil 803 and variousobstacles), a receiving system containing low-frequency receiving module804 (including low-frequency receiver coil 805 and low-frequencyreceiving circuit 806), and a signal strength detector 807 (a voltmeter,an oscilloscope, a spectrometer, etc.).

The principle of detecting voltage and distance curve (voltage-distancecurve) includes: the signal source 801 generates a sine wave signal witha fixed amplitude and of frequency f′, which is transmitted by thetransmitter coil 803 in the mobile terminal 802, and the signal passesthrough or is diffracted through the typical mobile terminal andobstacles. The low-frequency receiver module 804 converts the receivedlow-frequency signal and passes the signal to the signal strengthdetector 807 through a dedicated signal line, and the signal strengthdetector 807 detects the received voltage. By changing the distance ofthe mobile terminal, the low-frequency receiving module receivescorresponding signals from the mobile terminal and obstacles, and thecurve of the detection voltage changes with the distance can beobtained, i.e., the voltage-distance curve, under the frequency f′. Themobile terminal and obstacles can be changed to obtain curves ofdifferent mobile terminals, and the frequency f′ can also be changed toobtain different curves.

FIG. 25 shows the voltage-distance curves detected by the system in FIG.24. As shown in FIG. 25, under the second low-frequency channelcommunication mode, the voltage-distance curves have similar patterns tothose under the first low-frequency channel communication mode, thevoltage detected by the RF card reader decreases monotonically with thedistance.

In Step c2, the relevant parameters of the low-frequency magneticinduction circuit, low-frequency amplifier circuit, and filter circuitin the low-frequency receiver module of the RF card reader can bedetermined as follows:

Step c201, under a selected operating frequency, a selected modulationscheme and a selected coding mode, first selecting the typical noiseterminal and the magnetic detection and the amplification gain that areeasy to achieve by the RF card reader.

Step c202, detecting inherent noise voltage amplitude Vn′ of thedetection voltage of the RF card reader when the RF card is not sendingthe first low-frequency alternating magnetic field signal.

Step c203, detecting the detection voltage Vr of the card reader whenthe RF card is sending the low-frequency alternating magnetic fieldsignal using the selected modulation and coding and the selectedtransmission magnetic flux density; adjusting the parameters of thelow-frequency magnetic induction circuit, low-frequency amplifiercircuit, and filter circuit in the RF card reader, such thatVr/Vn′>SNR′, where SNR′ is the minimum signal-noise-ratio at which theRF card reader can perform decoding within the preset communicationrange. In this step, the adjustments of the parameters of thelow-frequency magnetic induction circuit and the low-frequency amplifierand filter circuit are mainly to adjust the sensitivity of thelow-frequency magnetic induction devices, such as the area and thenumber of turns of the low-frequency receiver coil, and the gain and thebandwidth of the low frequency of the low-frequency amplifier and filtercircuit.

In Step c2, the second transmission parameters of the RF card alsoinclude the low-frequency coding mode, modulation mode, andlow-frequency transmission magnetic flux density Bc, and thetransmission parameters may be determined through the following Steps.

Step c211, selecting any coding mode without an average DC component,such as Manchester, Differential Manchester, NRZ, etc.

Step c212, selecting no modulation or a carrier modulation mode withoutamplitude change. The carrier modulation mode can use any modulationmethod without amplitude change. For example, the carrier wave may be asine wave carrier, a pulse carrier, or a triangle wave carrier, etc. Themodulation may be on-off keying (OOK), phase shift keying or frequencyshift keying (FSK), etc. In the no-modulation mode, the encoded basebandsignal is directly driven by the driver circuit and transmitted by thetransmitter coil.

Step c213, selecting the transmission magnetic flux density Bc of thesecond low-frequency channel. Specifically, under a selected operatingfrequency that is less than f0, a selected modulation scheme and aselected coding mode, first selecting the typical noise terminal and themagnetic detection and the amplification gain that are easy to achieveby the RF card reader; then detecting inherent noise voltage amplitudeVn′ of the detection voltage of the RF card reader when the mobileterminal is not sending the low-frequency alternating magnetic fieldsignal. Further, detecting the detection voltage Vr of the RF cardreader when the mobile terminal is sending the low-frequency alternatingmagnetic field signal using the selected modulation and coding mode. Thetransmission magnetic flux density Bc is selected such that Vr/Vn′>SNR′,where SNR′ is the signal-noise-ratio of the low-frequency signal of theRF card reader. In general SNR′ value may be selected as large aspossible, as not to cause the transmission power of RF communicationdevice to be too high. For example, the SNR′ may be selected as SNR′=10.After the SNR′ is determined, Bc is also determined as described above.

Step d2, after receiving the second low-frequency alternating magneticfield signal, the RF card reader obtains the identification informationcarried by the signal, and compares the identification information ofthe RF card reader in the second low-frequency alternating magneticfield signal with its own identification information. If they are thesame, the RF card reader combines its own identification information andthe identification information of the RF card, which can be used for theRF communication address and channel parameters of the RF communicationto conduct card transaction with the terminal equipped with the RF card.

As used herein, card transaction not only refers to any electronicpayment, but also refers to any other communications process using RFchannels, such as recharging, consuming, and identity authentication,etc. That is, the card transaction refers the communication conductedthrough the RF channels, especially the short-range or near-fieldcommunication over RF channels.

Thus, through the above Steps of a2, b2, c2, and d2, secure andeffective control of the communication distance can be realized by usingthe two-way low-frequency magnetic field detection techniques, and noterminal calibration is needed.

In the disclosed embodiments, the frequency of the low-frequencyalternating magnetic field signal may be in the low frequency band,very-low frequency band, or ultra-low frequency band. For example, theultra-low frequency band may be in a range of approximately 300 Hz 3000Hz, the very-low frequency band may be in a range of approximately 3KHz˜30 KHz, and the low frequency band may be in a range ofapproximately 30 KHz˜300 KHz. In certain embodiments, the frequency ofthe low-frequency alternating magnetic field signal can be in a range ofapproximately 300 Hz˜50 KHz, such as 10 KHz, 15 KHz, 20 KHz, 25 KHz or30 KHz. For example, the frequency of the first low-frequencyalternating magnetic field signal can be approximately 500 Hz, 1 KHz,1.5 KHz, 2 KHz, 2.5 KHz, 3 KHz, 4 KHz, 5 KHz, 10 KHz, 20 KHz or 30 KHz;and the frequency of the second low-frequency alternating magnetic fieldsignal can be approximately 10 KHZ, 20 KHZ, 25 KHZ, 30 KHZ, 35 KHZ, or40 KHZ.

Thus, according to the disclosed embodiments, an RF card reader and amethod for communication distance control between the RF card reader andthe mobile terminal with the RF card is provided. The method uses thetwo-way low-frequency magnetic field communication and two-wayhigh-speed RF communication, avoiding the antenna problem and theterminal signal attenuation difference problem caused by only using the13.56 MHz frequency for two-way communication and distance control inNFC systems. This method can also prevent the RF card reader beingtampered, such as increasing the low-frequency RF transmission power orRF receiver sensitivity of the RF card reader, to impact user experienceand effectiveness on the card transactions. According to the disclosedembodiments, the RF card reader uses the first low-frequency channel tosend its unique identification IDr (i.e., the aforementionedidentification information) to the RF card, and the RF card uses thesecond low-frequency channel to send its unique identification IDcappended to the identification IDr to the RF card reader. The RF cardreader determines the correctness returned IDr, and achieves a uniquebinding between the RF card and the RF card reader. After the binding,the RF card and the RF card reader can perform high-speed communicationof large amount of data using the two-way RF channel, until thecompletion of the card transaction.

The implementation of the communication system is illustrated asfollows.

(1), The communication frequency f0 of the first low-frequency channelcan be selected using previously-describe methods, the details of whichare not repeated herein.

(2), the Process for Distance Control and Connection the RF Card to theCard Reader.

The card reader switches back and forth between a low-frequencytransmitting state and a low-frequency receiving state at a fixedperiod. When in the transmitting state, the RF card reader transmits thefirst low-frequency alternating magnetic field signal at a frequency nohigher than the selected frequency f0 using preconfigured transmissionparameters and based on the distance control target. The firstlow-frequency alternating magnetic field signal carries a data framebased on modulated signal or direct baseband signal. The data framecontains a unique identifier IDr of the RF card reader (of course canalso be other identification information). When the mobile terminal withthe RF card is placed around the card reader, the low-frequencyalternating magnetic field signal penetrates the mobile terminal andreaches the RF card. The RF card detects and amplifies the low-frequencyalternating magnetic field signal at each distance point into a voltagesignal of constant amplitude and corresponding to the distance point.

When the voltage value is lower than the preset threshold value in theRF card, it indicates that the terminal does not enter into a valid cardtransaction range, and card transactions are not allowed. When thevoltage amplitude is higher than the preset voltage threshold of the RFcard, it indicates that the terminal enters into the valid cardtransaction range, the RF card parses the information in the magneticfield signal and obtains the identifier IDr of the RF card reader. TheRF card then sends the second low-frequency alternating magnetic fieldsignal carries a data frame based on modulated signal or direct basebandsignal. The data frame contains the unique identifier IDr of the RF cardreader and a unique identifier IDc of the RF card. The RF card readerparses the magnetic field signal and obtains the IDr and the IDc, andcompares with the received IDr and its own IDr. If the received IDr isthe same as its own IDr, it indicates that the terminal enters into thevalid card transaction range. The RF card reader combines the IDr andthe IDc to generate the RF communication address and initiate cardtransaction. Further, when a card transaction is initiated, the RF cardreader is no longer switching between the low-frequency transmittingstate and the low-frequency receiving state periodically. Instead, theRF card reader continuously transmits the low-frequency magnetic fieldsignal to ensure that the mobile terminal with the RF card and the RFcard reader are always within the valid card transaction range. Thus,the RF card and the RF card reader can be uniquely bond, with both sidesusing the unique combined address (IDr, IDc) to identify each other.After the binding, the communication process for data exchange using theRF channel is less likely to generate errors. That is, after the RF cardis successfully bond with or connected to the card reader, the distancecontrol process is completed, and a subsequent card transaction can becarried out on the RF channel until the end of the transaction.

(3), the Transaction Process.

The RF card and the RF card reader establish the unique and reliablecommunication link through the RF channel. Based on the communicationlink, the two sides can complete the authentication required by thetransaction and other processes required by the transaction. All ofthese processes can be accomplished by a fast RF channel. Because theabove described process can ensure that the connection can only be madewithin a predetermined distance range, the entire transaction processcan also be communication limited within the predetermined distancerange.

FIG. 26 shows an exemplary communication system according to disclosedembodiments. As shown in FIG. 26, the communication system consists oftwo parts: the card reader 005 and the RF card 006. The RF card 006 isplaced inside a mobile terminal and interacts with the mobile terminalthrough terminal communication interfaces.

As shown in FIG. 26, the RF card reader 005 may comprise the followingmodules: a first main processor 052, responsible for the card reader lowfrequency and high frequency control and processing other protocols, thefirst main processor 052 can connect to the external communicationinterface via the interface circuit 051 or directly; an encoding circuit053 responsible for coding the low-frequency frame data bit by bit; amodulation circuit 054 responsible for modulating the symbol streamoutputted by the encoding circuit against a carrier wave to generate amodulated signal to the drive circuit 055 or for directly sending theencoded signal to the drive circuit 025 if no modulation is used; adrive circuit 055, responsible for driving the low-frequency transmittercoil 056 to generate the low-frequency alternating magnetic field signal007; a low-frequency magnetic induction circuit 056 comprising a PCBcoil, a wire coil, a giant magnetoresistive device, a Hall device, orother circuit elements capable of sensing magnetic field changes,responsible for inducing and converting the low-frequency alternatingmagnetic field signal 008 into an electrical signal; a low-frequencyamplifier and filter circuit 058 responsible for amplifying theelectrical signal detected by the low-frequency magnetic inductioncircuit and filtering out the noise component; a demodulation circuit059 responsible for demodulating the low-frequency signal with the noisecomponent filtered out to generate the encoded signal transmitted by theencoding circuit 063 of the RF card 006, and sending the demodulatedencoded signal to the first main processor 052. The first main processor052 is responsible for decoding processing. An RF transceiver circuit0511 is responsible for completing RF two-way communication with the RFtransceiver module of the RF card 006 through the RF antenna 0510.

As shown in FIG. 26, the RF card 006 may comprise the following modules:a second main processor 062 responsible for controlling low-frequencyand RF modules and processing other protocols and also responsible forcommunicating with the mobile terminal; an SIM/TF/SD card module 061being internal SIM/TF/SD card module of the mobile terminal, the moduletype is determined by the specific type of the card; a low-frequencymagnetic induction circuit 067 comprising a PCB coil, a wire coil, agiant magnetoresistive device, a Hall device, or other circuit elementscapable of sensing magnetic field changes, responsible for inducing andconverting the low-frequency alternating magnetic field signal 007 intoan electrical signal; a low-frequency amplifier and filter circuit 068responsible for amplifying the electrical signal detected by thelow-frequency magnetic induction circuit into a low-frequency detectionvoltage signal; a threshold judgment and demodulation circuit 069responsible for comparing the value of the low-frequency detectionvoltage signal the value with the preset threshold value. If the valuedoes not reach the threshold, demodulation is not performed and any cardtransaction is not allowed. If the value reaches the preset thresholdvalue, the demodulation is performed and the demodulated signal is sentto the second main processor 062. The RF card 006 also includes anencoding circuit 063, responsible for encoding a low-frequency frame bitby bit; a modulation circuit 064 responsible for modulating the symbolstream outputted by the encoding circuit against a carrier wave togenerate a demodulated signal to the drive circuit 065 or for directlysending the encoded signal to the drive circuit 065 if no modulation isused; the drive circuit 065, responsible for driving the low-frequencytransmitter coil 066 to generate the low-frequency alternating magneticfield signal 008; and an RF transceiver circuit 0611 responsible forcompleting RF two-way communication with the RF transceiver module ofthe card reader 005 through the RF antenna 0610.

The communication system achieves distance detection and control withoutcalibration by determining the low-frequency communication thresholdfrom the mobile terminal to the card reader and the low-frequencycommunication distance limitation from the mobile terminal to the RFcard reader. That is, the RF card reader 005 transmits the firstlow-frequency alternating magnetic field signal 007 in accordance withthe preset transmission parameters, and the RF card 006 receives themagnetic field signal and converts it into a low-frequency detectionvoltage signal, and uses a preset threshold value to determine whetherthe terminal enters the preset valid distance range set by the RF cardreader 005. After entering the valid distance range, the RF card 006transmits the second low-frequency alternating magnetic field signal 008to the RF card reader 005. The RF card reader 005 receives the magneticfield signal and analyzes the data in the received signal. If the datais legitimate, it indicates that the RF card reader 005 and the RF card006 enter into the valid card transaction range set by the system.Before the RF card reader receives the low-frequency magnetic fieldsignal, the relevant parameters of its low-frequency receiver module canbe adjusted such that the signal-to-noise-ratio of the RF card reader isgreater than the minimum signal-to-noise-ratio SNR′ at which the RF cardreader can still perform decoding.

Thus, the unique binding between the RF card reader 005 and the RF card006 is realized by using the combination of the two-way low-frequencycommunication and two-way RF communication. That is, the RF card reader005 uses the first low-frequency channel to send its uniqueidentification IDr to the RF card 006, and the RF card 006 uses thesecond low-frequency channel to send its unique identification IDcappended to the identification IDr to the RF card reader 005. The RFcard reader 005 determines the correctness returned IDr, and achieves aunique binding between the RF card 006 and the RF card reader 005. Afterthe binding, the RF card 006 and the RF card reader 005 can performtwo-way high-speed communication of large amount of data using the RFchannel.

The operational flow of the communication system associated with the RFcard reader is illustrated as follows.

Step A010: distance detection and control process. The first mainprocessor 052 of the RF card reader 005 generates a data framecontaining a unique identifier IDr of the RF card reader 005 and sendsit to the encoding circuit 053 to be encoded. The encoded signal ismodulated by the modulation circuit 054 and passed to the drive circuit055 or is directly passed to the drive circuit 055 without modulation,the modulated voltage is sent to the low-frequency transmitter coil 056.Based on preconfigured frame format, modulation and coding schemes, anddriving capability, the transmitter coil 056 transmits the firstlow-frequency alternating magnetic field signal 007 at the presetintensity Bc in accordance with the selected frame format andtransmission parameters.

When the mobile terminal is placed around the RF card reader 005, thefirst low-frequency alternating magnetic field signal 007 penetrates theterminal and reaches the RF card 006. The low-frequency magneticinduction circuit 067 of the RF card 005 detects the low-frequencymagnetic field signal into an electrical signal. The electrical signalis amplified and filtered out noise component by the low-frequencyamplifier circuit 068 to generate a low-frequency detection voltage.When the detection voltage is less than the preset receiving thresholdvalue, card transactions are not allowed. When the detection voltage isgreater than or equal to the preset receiving threshold value, itindicates that the terminal enters into the predetermined effectivecommunication distance range of the RF card reader 005. The thresholdjudgment and demodulation circuit 069 parses the detection voltagesignal to obtain IDr and to send it to the second main processor 062.

The second main processor 062 composes a data frame including the uniqueidentification IDc of the RF card 006 and the unique identification IDrof the RF card reader 005 and sends the frame to the encoding circuit063. The encoded signal is modulated by the modulation circuit 064 andpassed to the drive circuit 065, or is directly passed to the drivecircuit 065 if no modulation is used. The drive circuit 065 drives thelow-frequency transmitter coil 066 to transmit the low-frequencyalternating magnetic field signal 008 based on preconfigured frameformat, modulation and coding mode, and transmission magnetic fieldintensity.

The low-frequency magnetic induction circuit 056 of the RF card reader005 detects the low-frequency magnetic signal into an electrical signal,which is then amplified and filtered out the noise component by thelow-frequency amplifier and filter circuit 058 to a low-frequencydetection voltage. The relevant parameters of the low-frequency magneticinduction circuit 056 and the low-frequency amplifier and filter circuit058 can be adjusted such that the receiving signal-to-noise-ratio of theRF card reader 005 is greater than the minimum signal-to-noise-ratioSNR′ at which the RF card reader can still perform decoding. The voltagesignal is processed by the demodulation circuit 059 to obtain theoriginal encoded signal sent by the RF card 006, which is send to thefirst main processor 052 for decoding processing. After decoding, theIDr and the IDc is obtained, the first main processor 052 determineswhether the received IDr and its own IDr are the same. If the receivedIDr and its own IDr are not the same, card transactions are not allowed.If the received IDr and its own IDr are the same, it indicates that theRF card reader and the RF card enter into the preconfigured valid cardtransaction range.

The frame format in Step A010 can be defined as follows:

FIG. 27 illustrates a low-frequency data frame transmitted by the RFcard reader. As shown in FIG. 27, the RF card reader low-frequency dataframe includes the following.

Preamble: 8 bits, usually FFH, for frame synchronization.

Control field: eight bits, providing information for reading the frame,such as length, data type, etc., reserved bits can used for expansion.

IDr: N bits, the unique identifier of the RF card reader, specified bythe control field, where N is a natural number.

CRC: the checksum for the control field and the IDc, CRC checksum orother format can be used.

FIG. 28 illustrates a low-frequency data frame transmitted by the RFcard. As shown in FIG. 28, the RF card low-frequency data frame includesthe following.

Preamble: 8 bits, usually FFH, for frame synchronization.

Control field: eight bits, providing information for reading the frame,such as length, data type, etc., reserved bits can used for expansion.

IDr+IDc: N bits, the unique identifier of the RF card reader and theunique identifier of the RF card, specified by the control field, whereN is a natural number.

CRC: the checksum for the control field and the IDr+IDc, CRC checksum orother format can be used.

The above-described frame formats are only examples, any frame formatcontaining the unique identifier of the RF card and/or the uniqueidentifier of the RF card reader can be used. The unique identifier canbe a random number of sufficient length, the card reader may also bemanually assigned a unique code, or other methods may be used togenerate the unique identifier.

Step A020: as described in Step A010, after the RF card readerdetermines that the received IDr information and its own IDr informationare consistent, it indicates that the RF card reader and the RF cardenter a valid card transaction range preconfigured by the system. Thefirst main processor 202 set the combination of the IDr and IDc as theRF communications address, so that the RF card with identification IDcand the RF card reader with identification IDr can be uniquely bondtogether, using the combination address (IDr, IDc) to uniquely identifyeach other. After the binding, the communication process over the RFchannel is less likely to generate errors. After the RF card issuccessfully connected to or bond to the RF card reader, the distancecontrol process is completed, and the subsequent card transactionprocess can be carried out on the RF channel.

The unique identifier IDc of the RF card in Step A020 can be a uniqueidentifier pre-stored in the nonvolatile memory (NVM) of the RF card, ora random number with a sufficient length internally generated by the RFcard.

Step A030: transaction process. The card reader 005 and the RF card 006establish a reliable and unique communication link through the RFchannel. Based on the link, the two sides can complete theauthentication required by the transaction and other processes requiredby the transaction. All of these processes can be accomplished by a fastRF channel. Because Steps A010˜A020 can ensure that the connection tothe RF card 006 can only be made within a predetermined distance range,the entire transaction process can also be communication limited withinthe predetermined distance range. The transaction process may be a POStransaction process, the details are omitted herein.

The low-frequency signal detection circuit 057 and 067 of the RF cardreader 005 and the RF card 006 may each comprise a PCB coil, a wirecoil, a GMR device, or a Hall device. Other sensing device may also beused, so long as the device is capable of converting the magnetic fieldinto an electrical signal. The low-frequency signal detection circuit067 of the RF card 006 needs to be disposed within the card, and thelow-frequency signal detection circuit 057 of the RF card reader 005should have higher magnetic induction sensitivity.

Thus, the disclosed communication system can use low-frequencyalternating magnetic field to achieve distance detection and control,and to achieve two-way low-frequency communication between the RF cardreader to the RF card. The RF channel can be used in combination withthe low-frequency two-way communication to achieve reliable and uniquebinding, and the RF channel can be used to achieve high-speed datacommunication between the RF card reader and the RF card. Certaincharacteristics include: (1) the mobile terminal does not need to bemodified, only needs to replace the SIM/TF/SD card inside the mobileterminal and the reliable two-way distance communication can beachieved; (2) because the current provided by the RF card is limited,the communication distance of the low-frequency signal is limited, whichcan prevent the transmission power of the RF card being tampered orincreased, and the communication distance can be effectively controlledwithin a predetermined range. In addition, the RF transceiver circuit isplaced within the RF card to achieve two-way high-speed communicationwith the RF transceiver circuit with the card reader. Because theantenna of the RF circuit is very small, it can be easily integratedinto the SIM/TF/SD card.

According to the disclosed embodiments, after selecting the frequency f,the low-frequency transmission magnetic flux density Br of the RF cardreader, and the minimum receiving signal-to-noise-ratio SNR′ of the RFcard reader, the RF card reader used in the above system can performeffectively distance control on the mobile terminal equipped with the RFcard and complete the card transaction. As an extension, frequency f mayalso be selected above the frequency f0 or the minimum receivingsignal-to-noise-ratio of the RF card reader is less than SNR′, which maycause reduced performance, reduced distance control accuracy, and/orreduced communication success rate. However, such use does not conflictwith the disclosed invention, and merely an extension with modifiedperformance.

FIG. 29 illustrates another structural diagram of the RF card reader. Asshown in FIG. 29, the RF card reader includes four parts, an interfacecircuit 1000, an RF transceiver module 1100, a low-frequency transmittermodule 1200, and a low-frequency receiver module 1300. The interfacecircuit 1000 is configured to interface with an upper-level controllerfor interface communication; the RF transceiver module 1100 includes aRF transceiver circuit 1102, an RF antenna 1103, and a main controller1101; the low-frequency transmitter module 1200 includes a codingcircuit 1201, a modulation circuit 1202, a drive section 1203, alow-frequency transmitter coil 1204, and the main controller 1101; thelow-frequency receiver module 1300 includes a low-frequency magneticinduction circuit 1301, a low-frequency amplifier and filter circuit1302, a low-frequency demodulation circuit 1303, and the main controller1101. The RF transceiver module 1100, the low-frequency transmittermodule 1200, and the low-frequency receiver module 1300 can share thesame main controller. The drive section 1203 includes a drive circuitand an adjusting circuit. Thus, the RF card reader in FIG. 29 is similarto the RF card reader in the communication system shown in FIG. 26.However, in FIG. 29, the main controller 1101 replaces the first mainprocessor 052 in the FIG. 26.

The low-frequency transmitter module is operated at a predeterminedfrequency less than the highest frequency f0 of the first low-frequencychannel of the system. The selection of the parameters of thelow-frequency magnetic induction circuit in the low-frequency receivermodule and low-frequency amplifier and filter circuit is made such thattheir signal-to-noise-ratio is greater than the minimum decodablesignal-to-noise-ratio SNR′. The RF card reader transmits the firstlow-frequency alternating magnetic field signal having a preconfiguredconstant amplitude or differential amplitude. The amplitude of thelow-frequency alternating magnetic field signal corresponding to thepreset physical communication distance, and the deviation of theamplitude of the low-frequency alternating magnetic field signal is lessthan the preset fluctuation value δ_(R). The details of the amplitudeand the physical distance are described previously and are omittedherein.

The low-frequency transmitter coil 1204 is configured to transmitlow-frequency magnetic field signal, and may mainly include a wire coilor a PCB coil.

The main controller 1101 is responsible for controlling the entire RFcard reader, including the low-frequency transmitter module 1200, thelow-frequency receiver module 1300, and the RF transceiver module 1100.

The transceiver circuit 1102 is configured to transmit and receive RFsignals. The frequency of the RF communication may be primarily in theUHF frequency band, especially 2400 Mhz˜2483 MHz band. Other frequencybands, such as 433 MHz, 900 MHz, and 5 GHz, etc., may also be used.

The RF antenna 1103 is responsible radiating and receiving the RFenergy; the encoder circuit 1201 is used to perform certain encodingprocessing on the low-frequency magnetic field signal; the modulationcircuit 1203 is used to modulate the encoded signal on a carrier wave;the drive section 1203 includes a drive circuit and an adjustmentcircuit where the drive circuit is mainly responsible for amplifying thelow-frequency magnetic field signal I and enhancing its driving ability,and the adjustment circuit is mainly responsible for adjusting thedeviation of the low-frequency magnetic field signal strength. Thedriver circuit can include DAC (Digital-to-Analog Converter) andoperational amplifiers (op amp) for generating and amplifying squarewaves, sine waves, triangle waves, etc., or can include circuitrycomprising resistors, capacitors, and op amps for generating andamplifying square waves, sine waves, triangle waves, etc. The adjustmentcircuit can adjust the output voltage of the driving circuit or adjustthe resistance of the load.

The low-frequency magnetic induction circuit 1303 is responsible forinducing and converting the second low-frequency alternating magneticfield signal transmitted by the mobile terminal with the RF card throughthe second low-frequency channel into an electrical signal. The maximumoperating frequency of the signal is f0′. The frequency f0′ can bedetermined similarly to the previous descriptions, just with differenttarget range of the communication distance. The communication distancetarget range of the second low-frequency channel is Din˜Din+Dv′(Dv′>Dv). Further, the low-frequency magnetic induction circuit maycomprise a PCB coil, a wire coil, Hall device, or a giantmagnetoresistive device.

The low-frequency amplifier and filter circuit 1302 is responsible foramplifying the electrical signal detected by the low-frequency magneticinduction circuit and filtering out the noise component, so as to obtaina maximum low-frequency receiving signal-to-noise-ratio. The amplifiercircuit can comprise various op amps and resistors, and the filtercircuit may comprise

The low-frequency circuit 1302 is responsible for amplifying andfiltering the low-frequency electrical signal to the magnetic sensorcircuit for receiving the pre-amplification and filtering of noise so asto obtain the maximum signal to noise ratio of the received frequency,amplified by a variety of circuits can be put into operation, resistors,the filter circuit may be a passive filter formed by resistors andcapacitors composed or an active filter formed by resistors, capacitors,and op amps.

The demodulation circuit 1301 is responsible for demodulation process ofthe low-frequency amplified signal. The demodulation circuit may be ananalysis circuit processing a baseband signal without modulation andmainly comprises comparators and resistors, or the demodulation circuitmay be a signal demodulation circuit processing modulated signalscorresponding to the modulation format used by the RF card. Thedemodulation format can be selected as one of the on-off keying (OOK),phase Shift keying (PSK), or frequency shift keying (FSK), etc.

When selecting low-frequency coil for the low-frequency magneticinduction circuit in the RF card reader, the low-frequency receiver coiland the low-frequency transmitter coil can share the same coil. FIG. 34shows an exemplary coil sharing mode.

As shown in FIG. 34, the system comprises the main controller 1101, thelow-frequency transmitter module 1200, the low-frequency receiver module1300, the low-frequency coil 1801, and an analog switch 1802. The maincontroller 1101 provides a control signal SW, which is a square wavesignal with alternating high and low cycles, whose period may beadjusted according to the real applications. The control signal SWcontrols the analog switch.

For example, when the control signal is high, the analog switch iscontrolled to connect the low-frequency transmitting module; when thecontrol signal is low, the analog switch selects the low-frequencyreceiving module. Thus, the low-frequency receiver coil and thelow-frequency transmitter coil can share the same coil, saving space andproduct cost. The analog switch can be an SPDT or DPDT switch or anyappropriate controllable switch.

To ensure the consistency among the RF card readers in mass production,a system for adjusting the deviation of the RF card readers may beestablished. The system detects and adjusts the deviation or errors ofeach RF card reader to ensure the consistency of each RF card reader,and to ensure the card transaction distance is controllable.

FIG. 33 shows an exemplary RF card reader error correction system. TheRF card reader error correction system includes RF card reader to becorrected 1702, and magnetic field intensity detection device 1701positioned above the RF card reader to be corrected at a predeterminedheight Dc.

Based on the error correction system shown in FIG. 33, an RF card readererror correction process can include the following steps:

Step 1, setting the measurement target Hs and error range He of themagnetic field intensity detection device. Under the standard magneticfield intensity detection device, the error correction magnetic fieldintensity range of the correcting RF card reader is [Hs−He, Hs+He],where He<δ_(R), δ_(R) is the default error value, the smaller the He,the greater the system margin.

Step 2, during RF card reader testing, the RF card reader to becorrected is transmitting low-frequency magnetic field signal, themagnetic field intensity detection device determines the magnetic fieldintensity of the received low-frequency magnetic field signal, andadjust the transmitting adjustment circuit on the RF card reader to becorrected, such that the magnetic field intensity of the corrected RFcard reader is within the error correction magnetic field intensityrange of [Hs−He, Hs+He].

The error correction system may be a separate system, or may be withinthe low-frequency receiver module of the RF card reader, so as torealize the self-error-correction function of the RF card reader.

FIG. 29 shows an exemplary RF card reader, and the error correctionmethod is described in the followings:

Step 10, set the radio frequency reader low frequency receiver modulemeasuring error range goals Hs and He, the field intensity in the errorcorrection low frequency range of the RF receiver module under thereader to [Hs−He, Hs+He], where He<δ_(R), the smaller the He, thegreater the system margin. The low-frequency receiver module, as shownin FIG. 29, comprises sequentially connected the controller 1101, thedemodulation circuit 1301, the low-frequency amplifying and filteringcircuit 1302, and the receiver coil 1303. The principle for detectingthe magnetic field intensity is to use the high voltage and low voltageratio detected by the demodulation circuit to determine thecorresponding field intensity.

Step 20, during RF card reader testing, the low-frequency transmittercoil of the RF card reader transmits low-frequency magnetic fieldsignal, the low-frequency receiver module determines the magnetic fieldintensity of the received low-frequency magnetic field signal, andadjust the transmitting adjustment circuit on the RF card reader, suchthat the magnetic field intensity of the RF card reader is within theconfigured error correction magnetic field intensity range of [Hs−He,Hs+He].

The RF card reader can also detect whether there is interference RFdevice around the RF card reader and send alarms if there is.Specifically, the RF interfering device detection method can include thefollowings: when working with a legitimate RF card, searching whetherthere is any low-frequency signal or RF signal; performing decodingprocessing on the detected low-frequency signal or RF signal;determining whether the information carried in the low-frequency signalor RF signal contains only the identification code of the legitimate RFdevice. If yes, it indicates that there is no interfering RF devicenearby, otherwise there is nearby interfering RF device. Further, the RFcard reader can detect the signal strength of the received low-frequencysignal or RF signal and, based on the signal strength of the receivedlow-frequency signal or RF signal, determine the distance between itselfand the interfering RF device. If the nearby interfering RF device iswithin the preset safe distance, an alarm can be sent out.

Further, according to the disclosed embodiments, a distance controlmethod based on low-frequency alternating magnetic field may also beprovided using the above RF card reader. Thelow-frequency-alternating-magnetic-field distance control method caninclude the following steps.

Step A, switching back and forth between a low-frequency transmittingstate and a low-frequency receiving state. When in the transmittingstate, the low-frequency transmitter module transmits the firstlow-frequency alternating magnetic field signal through the firstlow-frequency channel according to first transmission parameters. Thefirst low-frequency alternating magnetic field signal carries a uniqueidentifier IDr of the RF card reader. The first transmission parametersinclude the highest frequency f0 of the first low-frequency channel,encoding mode, modulation mode, and constant field intensity parameter.When being switched back to the receiving state, the low-frequencyreceiver module receives the second low-frequency alternating magneticfield signal from the RF card, the RF card is disposed within the mobileterminal.

The switching between the low-frequency transmitting state and thelow-frequency receiving state can be performed at a preset time period.

In Step A, the frequency of the first low-frequency alternating magneticfield signal is equal to or less than the highest frequency f0 of thefirst low-frequency channel. The highest frequency f0 of the firstlow-frequency channel may be selected as followings.

The lower the low-frequency alternating magnetic field frequency, thesmaller the attenuation difference after penetrating mobile terminals.Accordingly, from the frequency selection system, frequencies withsufficiently small difference can be selected to achieve distancecontrol without calibration. Using a standard signal source, a standardtransmitter coil transmits a low-frequency alternating magnetic field,the alternating magnetic field is received within various typical mobileterminals and obstacles. The transmission frequency is adjusted untilthe frequency f0 is found, so that the voltage received by the RF cardcauses the difference of the field intensity of different terminals andobstacles substantially within a preset fluctuation range δ_(T). Thisfrequency and the frequency band lower than the frequency belong to thefrequency band of the first low-frequency channel. If the frequency ishigher than f0, the system may need to be calibrated. In general, themore frequency higher than the f0, the more terminals need to becalibrated, and the more complexity the calibration. The frequencyselection may be performed one-time and, once selected, can be usedwithout change.

In Step A, in addition to frequency, other predetermined transmissionparameters of the first low-frequency alternating magnetic field signalcan be selected as follows.

Step A1: selecting the field intensity constant mode (i.e., constantfield intensity parameter), the field intensity constant mode includespeak field intensity constant amplitude and differential field intensityconstant amplitude. Step A2 can be performed to select the peak fieldintensity constant amplitude, while Step A3 can be performed to selectthe differential field intensity constant amplitude, the deviation ofthe constant field intensity parameter is less that the preset deviationδ_(R).

The typical form of the DC or AC magnetic field with peak fieldintensity constant amplitude is shown in FIG. 30, which may be a DCmagnetic field or may be a square wave or sine wave magnetic field.

A low-frequency AC magnetic field with differential field intensityconstant amplitude is a low-frequency AC magnetic field with a constantmaximum magnetic field change rate, and its typical form is shown inFIG. 31. As shown in FIG. 31, under the transmission condition of atypical triangular-wave magnetic field with differential field intensityconstant amplitude, when the low-frequency magnetic induction device inthe RF card uses coils, such as an SIM card coil, the induced voltage isa square wave form.

The constant field intensity transmitted by the RF card reader can beused as reference field intensity for distance detection. Because thelow-frequency magnetic field changes with changing distances, the fieldintensity decays quickly and monotonously. Thus, the low-frequency fieldintensity, which changes with changing distances, around the RF cardreader changes can be used to measure the distance. By preciselycontrolling the deviation δ_(R) of the transmission field intensity ofeach RF card reader, the precision for measuring distance using the RFcard reader can be controlled. The typical δ_(R) is within the range of4 dB, i.e., the δ_(R) is typically less than 4 dB.

Step A2: with peak field intensity constant amplitude, selectingencoding mode, modulation format, and the driving voltage waveform;determining the target value of the low-frequency magnetic fieldintensity, thereby selecting the magnitude of the driving voltage, theadjustment parameters, the low-frequency transmitter coil resistance,the number of turns of the low-frequency transmitter coil. Measuring thelow-frequency magnetic field intensity under the selected parameters todetermine whether the deviation from the target value of thelow-frequency magnetic field intensity is within δ_(R). If yes, theselection of transmission parameters is complete. Otherwise, readjustingthe parameters of the drive circuit and the low-frequency transmittercoil, until the deviation between the measured low-frequency magneticfield intensity and the target value of the low-frequency magnetic fieldintensity is within δ_(R).

The selection process for the transmission parameters is shown in FIG.32. In Step A2, detailed selection can include the follows.

Encoding mode selection: under the condition of peak field intensityconstant amplitude, no specific requirement is needed for encoding. Theselection of encoding mode can be a one-time operation and no need tochange during operation once selected.

Modulation mode selection: under the condition of peak field intensityconstant amplitude, the modulation may be selected from constantenvelope modulation schemes such as FSK and PSK, etc. The selection ofmodulation mode can be a one-time operation and no need to change duringoperation once selected.

Driving voltage waveform selection: under the condition of peak fieldintensity constant amplitude, the driving voltage waveform preferably isa square wave driving voltage waveform. The selection of driving voltagewaveform can be a one-time operation and no need to change duringoperation once selected.

Target low-frequency magnetic field intensity selection: the targetlow-frequency magnetic field intensity can be determined based onspecific RF card reader applications. If it is a medium-long distanceapplication, higher magnetic field intensity may be required; if it is aclose distance application, lower magnetic field intensity may berequired.

Driving voltage amplitude selection: after selecting the targetlow-frequency magnetic field intensity, appropriate drive voltageamplitude can then be selected. The driving voltage amplitude can bemore than 60% of the full amplitude of the output voltage of the drivecircuit.

Adjustment parameters selection: the output voltage of the drive circuitor the resistance of the load can be adjusted, so that the low-frequencymagnetic field matches the preconfigured field intensity value.

Transmitter coil parameters selection: the transmitter coil can be awire coil or a PCB coil. The cross-sectional area of the low-frequencytransmitter coil may be greater than that of a mobile terminal, suchthat the SIM card in any different mobile terminal can be placed withthe low-frequency transmitter coil to ensure the stability andconvenience of the card transactions. The area of the low-frequencytransmitter coil (i.e., the area circulated by the coil) may be greaterthan 10 cm². For example, the cross-sectional area surrounded by thelow-frequency transmitter coil may be greater than 10 cm².

Further, for the low-frequency transmitter coil, with the same amount ofmagnetic flux, the number of turns needed is inversely proportional withthe driving voltage needed. The low-frequency transmitter coil can havemore than 10 turns. For example, the low-frequency transmitter coil canhave approximately 50 to 500 turns. The resistance of the low-frequencytransmitter coil may be greater than 10 ohms and, further, theresistance of the low-frequency transmitter coil can be approximately 50to 500 ohms.

After selecting the above parameters, the low-frequency magnetic fieldintensity is measured to determine whether its deviation from the targetvalue of the low-frequency magnetic field intensity is within δ_(R). Ifyes, the selection of transmission parameters is complete. Otherwise,the parameters of the drive circuit and the low-frequency transmittercoil are readjusted.

Step A3: with the differential field intensity constant amplitude,selecting encoding mode, modulation format, and the driving voltagewaveform; determining the target value of the low-frequency magneticfield intensity, thereby selecting the magnitude of the driving voltage,the adjustment parameters, the low-frequency transmitter coilresistance, the number of turns of the low-frequency transmitter coil.Measuring the low-frequency magnetic field intensity under the selectedparameters to determine whether the deviation from the target value ofthe low-frequency magnetic field intensity is within δ_(R). If yes, theselection of transmission parameters is complete. Otherwise, readjustingthe parameters of the drive circuit and the low-frequency transmittercoil, until the deviation between the measured low-frequency magneticfield intensity and the target value of the low-frequency magnetic fieldintensity is within δ_(R).

In Step A3, detailed selections can include the follows.

Encoding mode selection: under the condition of differential fieldintensity constant amplitude, the coding mode may be Manchester or NRZ,etc. The selection of encoding mode can be a one-time operation and noneed to change during operation once selected.

Modulation mode selection: under the condition of differential fieldintensity constant amplitude, the modulation may be selected fromconstant envelope modulation schemes such as FSK and PSK, etc. Theselection of modulation mode can be a one-time operation and no need tochange during operation once selected.

Driving voltage waveform selection: under the condition of differentialfield intensity constant amplitude, the driving voltage waveformpreferably is a triangular wave driving voltage waveform. The selectionof driving voltage waveform can be a one-time operation and no need tochange during operation once selected.

Other steps may be similar to those described in Step A2 under thecondition of peak field intensity constant amplitude, and detaileddescriptions are omitted.

Step B, parsing the second low-frequency alternating magnetic fieldsignal to obtain the identification code IDr of the RF card reader andthe identification code IDc of the RF card; comparing the IDr obtainedfrom the second low-frequency alternating magnetic field signal and theIDr in the transmitted first low-frequency alternating magnetic fieldsignal to determine whether they are the same. If yes, it can bedetermined that the RF card reader is within the predetermined distancerange.

In Step B, the RF card reader receives the second low-frequencyalternating magnetic analytical signal by the low-frequency receivermodule. The receiving parameters of the low-frequency receiver in the RFcard reader may include device selection of the magnetic inductioncircuit, the gain of the amplifier circuit and the bandwidth of thefilter circuit, which may be determined as follows.

Step B1, under the selected operating frequency, modulation scheme, andcoding mode of the RF card, first selecting the typical noise terminaland the magnetic detection and the amplification gain that are easy toachieve by the RF card reader.

Step B2, detecting inherent noise voltage amplitude Vn′ of the detectionvoltage of the RF card reader when the mobile terminal is not sendingthe low-frequency alternating magnetic field signal.

Step B3, at the preset farthest communication distance Din+Dv, measuringthe detection voltage Vr of the card reader, after amplifying andfiltering, when individual typical mobile terminals and obstacles issending the low-frequency alternating magnetic field signal using theselected modulation and coding mode and the selected transmissionmagnetic flux density; adjusting the parameters of the low-frequencymagnetic induction circuit, low-frequency amplifier and filter circuitin the RF card reader, such that Vr/Vn′>SNR′, where SNR′ is the minimumsignal-noise-ratio at which the RF card reader can perform decodingwithin the preset communication range. For example, the SNR′ may beselected as SNR′=10.

The following examples illustrate the method for determining the numberof turns of the low-frequency receiver coil, the gain of thelow-frequency amplifier circuit, and the bandwidth of the filter circuitin the low-frequency receiver module of the RF card reader in the StepB.

Step B11, with predetermined area of the low-frequency receiver coil,selecting the number of turns in the coil. The RF card transmits amagnetic field signal with a fixed field intensity and at a fixeddistance, and the corresponding low-frequency receivingsignal-to-noise-ratio of the RF card reader is measured, so that thesignal-to-noise-ratio is greater than SNR′. The test systemconfiguration may refer to FIG. 2.

Step B12, in the test system configuration shown in FIG. 2, introducinga noise source, especially an acoustic noise source. The noise hasconstant amplitude. The gain of the amplifier circuit, and the bandwidthof the filter circuit is selected such that the receivingsignal-to-noise-ratio of the RF card reader is greater than SNR′.

After determining that the RF card reader is within a preset distancerange, the RF card reader can use a combination address (IDr, IDc) asthe RF communication address and channel parameters of the RFcommunication, and conduct card transactions with the mobile terminalover the RF channel until the completion of the transaction. At the sametime, the low-frequency transmitter module of the RF card readercontinuously transmits low-frequency alternating magnetic field signalswith preconfigured transmission parameters.

The frequency range of the first low-frequency alternating magneticfield signal can be approximately 0-100 KHz and, further, the frequencyrange of the first low-frequency alternating magnetic field signal canbe approximately 0-10 KHz. The frequency range of the secondlow-frequency alternating magnetic field signal can be approximately0-100 KHz and, further, the frequency range of the second low-frequencyalternating magnetic field signal can be approximately 10-50 KHZ.

Embodiment Four

According to the disclosed embodiments, as used herein, a terminalrefers a terminal equipped with a second RF device, such as a mobileterminal; and a distance refers the distance between a first RF deviceand the second RF device, i.e., the distance between the first RF deviceand the terminal equipped with the second RF device.

In certain embodiments, with respect to the distance control problemsfor performing card transactions between the second RF device(especially the RF card inside the terminal, such as an RF SIM card) andthe first RF device, there provides a communication system including afirst RF device capable of transmitting and receiving low-frequencyalternating magnetic field signals and transmitting and receiving RFsignals, and a corresponding second RF device capable of transmittingand receiving low-frequency alternating magnetic field signals andtransmitting and receiving RF signals. Communication methods of thecommunication system are also provided. According to the disclosedembodiments, low-frequency alternating magnetic field signal canpenetrate different terminals with small signal attenuation difference,and the current can be provided by the second RF device limited. Withoutaffecting the operation of the mobile terminal, the feature that thelow-frequency two-way communication distance is limited can be used fortwo-way distance control and limit, while high-frequency RF caneffectively penetrate the terminal to complete the high-speed tow-waycommunication for transactions.

According to the disclosed embodiments, detections of low-frequencyalternating magnetic field signals from the first RF device to themobile terminal (equipped with the second RF device) and oflow-frequency alternating magnetic field signals from the mobileterminal to the first RF device can be used to achieve two-way distancecontrol. More specifically, the first RF device transmits the firstlow-frequency alternating magnetic field signal in accordance with firstpreset transmission parameters through the first low-frequency channel.The frequency of the first low-frequency alternating magnetic fieldsignal is f. The second RF device detects the magnetic field signal ateach distance point and amplifies the signal into an electrical signal(e.g., a voltage signal or current signal) with constant amplitudecorresponding to the distance. Further, a preconfigured threshold valueis used to determine whether the mobile terminal enters into apredetermined valid card transaction range (also called effectivedistance range, i.e., the range allowing card transactions). Thepreconfigured first threshold value is the same for all mobileterminals, without the need for calibration. When the mobile terminalenters into a valid card transaction range, the second RF devicetransmits second low-frequency alternating magnetic field signal at apreset frequency f′ according to the second transmission parameters andthrough the second low-frequency channel. Only after the first RF devicecorrectly parses the second low-frequency alternating magnetic fieldsignal and determines that the second RF device is legitimate, RFcommunication and card transaction can begin. Thus, the two-waylow-frequency control can be achieved, as well as two-way distancecontrol and limiting. Thus, the first RF device and the second RF devicecan be uniquely bond together by combining the low-frequency two-waycommunication and two-way RF communication and, after the binding,two-way high-speed communication with large data can be completed viathe RF channel. Thus, the data communication distance (i.e., transactiondistance) between the terminal having the second RF device (e.g., amobile phone with an RF SIM card) and the first RF device can beeffectively controlled within a preset distance range, and nocalibration is needed for the terminals.

The disclosed communication methods may be applicable on anycommunication system including at least a first RF device and the atleast one second RF device. The communication method may comprise Stepsa4, Step b4, Step c4, Step d4, and Step e4 (Note: the step numbers areused only for convenience, do not have any particular meaning orindicate any particular order of the steps), which are described in thefollowings.

Step a4, the first RF device transmits a first low-frequency alternatingmagnetic field signal.

Specifically, the first RF device transmits a first low-frequencyalternating magnetic field signal through a first low-frequency channelbased on first preset transmission parameters. The first low-frequencyalternating magnetic field signal can carry identification informationof the first RF device. The first transmission parameters may includethe frequency of the first low-frequency alternating magnetic fieldsignal, and the frequency is equal to or less than the maximum operatingfrequency f0 of the first low-frequency channel in the system.

The identification information may be the identification code ID.

The lower the low-frequency alternating magnetic field frequency, thesmaller the attenuation difference after penetrating mobile terminals.Accordingly, from the frequency selection system (as shown in FIG. 35),frequencies with sufficiently small difference can be selected toachieve distance control without calibration. Using a standard signalsource, a standard magnetic transmitter coil transmits a low-frequencyalternating magnetic field signal. The second RF device inside thetypical terminal and obstacle receives the low-frequency alternatingmagnetic field signal, adjust the transmission frequency until findingthe frequency f0, so that the voltage received by the first RF device(this voltage is the voltage signal with a constant amplitudecorresponding to the distance from amplifying the low frequencyalternating magnetic field signal) causes the difference of the fieldintensity coming out from different terminals and obstacles, having thesame distance to the center point of the transmitter coil plane,substantially within a preset fluctuation range δ_(T). The frequency f0and the frequency band lower than the frequency f0 belong to thefrequency band of the first low-frequency channel communication mode,and no calibration is needed for any terminal at that system. If theoperating frequency (i.e., the frequency of the first low-frequencyalternating magnetic field signal) is higher than f0, the system mayneed to be calibrated. In general, the more operating frequency higherthan the f0, the more terminals need to be calibrated, and the morecomplexity of the calibration. The frequency selection may be performedone-time and, once selected, can be used without change.

FIG. 35 is a structural block diagram of a selection system forselecting the maximum operating frequency f0 of the first low-frequencychannel. As shown in FIG. 35, in one embodiment, the selection systemfor the first low-frequency channel maximum operating frequency f0comprises: a transmission system containing a signal source 085 and alow-frequency magnetic field transmitter coil 084, a receiving systemcontaining a typical mobile terminal 081 and obstacles, and a signalstrength detector 083 (a voltmeter, an oscilloscope, a spectrometer,etc.). A low-frequency receiver module 082 is disposed inside the mobileterminal 081. The signal source 085 may produce a variety of precisefrequency, waveform and amplitude signals. The principle of selectingthe frequency includes: the signal source 085 generates a sine wavesignal with fixed amplitude and of frequency f, which is transmitted bythe transmitter coil 084. The low-frequency receiver module 082 isdisposed inside the selected typical mobile terminal 081 or obstacle,and passes the received low-frequency signal to the signal strengthdetector 083 via a dedicated signal line, and the signal strengthdetector 083 measures the received voltage. By changing the distance ofthe mobile terminal, the curve of the detection voltage changes with thedistance can be obtained, i.e., the voltage-distance curves for themobile terminal or obstacle at the frequency f. The mobile terminal andobstacles can be changed to obtain curves of different mobile terminals,and the frequency f can also be changed to obtain different curves.

When the frequency f of the first low-frequency alternating magneticfield signal is less than frequency f0, different mobile terminalshaving the second RF device are within the valid communication distancerange, and no calibration is needed. Further, the maximum operatingfrequency f0 of the system's first low-frequency channel can bedetermined by the following steps.

Step 401, determining the system distance control target (Din, Dv) basedon the first low-frequency alternating magnetic field signal, where Dinmeans that all terminals (with the second RF device) within the range of0-Din are ensured for card transaction, and Dv denotes the distancefluctuation range. If the distance is within Din˜(Din+Dv), cardtransactions are allowed and, if the distance is greater than Din+Dv,card transactions are not allowed.

For example, (5 cm, 5 cm) means that all terminals within 5 cm areensured for card transactions, all terminals within 5 cm˜10 cm areallowed card transactions, and all terminals beyond 10 cm are notallowed card transactions. The distance control target may be determinedby specific applications, and (0˜Din+Dv) is called distance controlrange.

Step 402, determining the fluctuation range δ_(R) of the detectionvoltage in the second RF device that is caused by the first RF device.

That is, the fluctuation on the parameters of the low-frequencytransmitter circuit in the First RF device causes the fluctuation of thetransmission field intensity, causing the fluctuation of the detectionvoltage in the second RF device. The parameters include transmissiondrive voltage fluctuation, coil parameter fluctuations, temperatureimpact, and so on. The fluctuation range δ_(R) may be controlled by thecard reader design and production processes. Because the workingfrequency of the low-frequency transmitter circuit is substantially low,the fluctuation range δ_(R) can be controlled desiredly, such as lessthan 4 dB.

Step 403, determining the fluctuation range δ_(C) of the detectionvoltage caused by the second RF device itself.

That is, the fluctuation of the final detection voltage output caused bythe fluctuation on the parameters of the low-frequency receiver circuitin the second RF device. The parameters include the receiving antennadeviation, amplifier gain deviation, filter deviation, comparator or ADdeviation, temperature deviation, and noise, etc. The fluctuation rangeδ_(C) may be controlled by the RF card design and production processes.Because the operating frequency of the RF card low-frequencytransmission circuit is substantially low, the fluctuation range δ_(C)can be controlled desiredly, such as less than 4 dB.

Step 404, determining the voltage-distance curve of various typicalterminals and obstacles at the frequency f.

Before the Step 404, certain preparation work needs to be performed,i.e., selecting typical terminals and typical obstacles. Selection oftypical terminals is primarily based on the amount of metal orconductive structures of a terminal. The more metal included, the morethe attenuation. For example, typical terminals can be selected asterminals with plastic housing, with metal housing, with a thick metalshell, with a thin metal shell, with a large size, and with a smallsize, etc. The number of typical terminals is not limited, as long asthe selected typical terminals substantially cover the attenuationcharacteristics of the low-frequency alternating magnetic field signalcaused by terminals.

To avoid extraordinary deviation from any particular mobile terminal,the type of the mobile terminal may need to be confirmed inapplications. Each type of mobile terminal for transaction applicationsmay be tested to determine the attenuation characteristics of the typeof mobile terminal. Typical obstacles may be selected as standard shapeswith different materials, such as plastic, aluminum, copper, iron,stainless steel, and other common materials used in mobile terminals.The typical obstacles are placed between the first RF device and thesecond RF device as an equivalent obstacle of mobile terminalattenuation characteristics for measuring attenuation effect.

Step 405, based on the distance control target (Din, Dv), determiningfluctuation range δ_(A) of the detection voltage by the second RFdevice. The range δ_(A) equals to the difference between the voltagecorresponding to the point Din on the voltage-distance curve withaverage field intensity attenuation curve slope and obtained from thevoltage-distance curves of various typical terminals and obstacles andthe voltage corresponding to the point (Din+Dv).

FIG. 36 illustrates the total received detection voltage fluctuationrange δ_(A) determined by the distance control target (Din, Dv). Asshown in FIG. 36, the point Din corresponds to voltage value V1, and thepoint (Din+Dv) corresponds to the voltage value V2, and δ_(A)=V1−V2.

Step 406, determining the fluctuation range δ_(T) of the detectionvoltage of the second RF device caused by the mobile terminal. Theparameter δ_(T) represents the fluctuation range of the detectionvoltage of the second RF device caused by the attenuationcharacteristics of the terminal, δ_(T)=δ_(A)−δ_(R)−δ_(C).

FIG. 37 illustrates a voltage-distance curves and fluctuation range δ ofa typical terminal and obstacle. As shown in FIG. 37, thevoltage-distance curve corresponding to the maximum attenuation terminaland obstacle is called the maximum attenuation curve, andvoltage-distance curve corresponding to the minimum attenuation terminaland obstacle is called the minimum attenuation curve. The areasurrounded by the maximum attenuation curve and the minimum attenuationcurve is called the voltage-distance curve distribution area of thetypical terminal and obstacle. Provided that the voltage correspondingto any D on the minimum attenuation curve is V3, and the voltagecorresponding to any D on the maximum attenuation curve is V4, thenδ=V3−V4.

Step 407, calculating the maximum field intensity difference δ (alsocalled the fluctuation range) at various distances with the distancecontrol range of various typical terminals and obstacles. If δ isgreater than δ_(T), the frequency f is decreased and the method goes toStep 404. If δ is less than δ_(T), the frequency f is increased and themethod goes to Step 404. Further, if δ is equal to δ_(T), the currentfrequency f is equal to the frequency f0.

Thus, in the case of limited distance control target, the maximumoperating frequency f0 of the system's first low-frequency channel canbe determined. The first low-frequency channel may use a modulationmode, or may use another mode to directly transmit baseband signal mode.In operation, when the maximum main frequency component of the system isno greater than the frequency f0, and the distance control does not needto be calibrated.

An example is used to illustrate the process of determining frequencyf0. FIG. 38 shows 5 voltage-distance curves of 5 typical mobileterminals at frequency f of 3.3 KHz. As shown in FIG. 38, the systemdistance control target is (5 cm, 5 cm), the voltage fluctuation rangeof the system range at range 0˜10 cm is about 40 dB, and the fluctuationof the detection voltage in the second RF device caused by the First RFdevice and the second RF device is both 4 dB, i.e., δ_(R)=δ_(C)=4 dB,δ_(A)=20 dB, δ_(T)=δ_(A)−δ_(R)−δ_(C)=12 dB. Assuming the 5 terminals canbe used to represent all terminals used in the system, the maximumfluctuation at each distance of the curves is approximately 12 dB. Thus,the maximum frequency f0 of the system's first low-frequency channel maybe determined as f0=3.3 KHz.

Further, the first transmission parameters can also include modulationmode, coding mode, and transmission magnetic flux density Br. The firsttransmission parameters are selected to ensure that the signal detectedand amplified by the second RF device from the first low-frequencyalternating magnetic field signal transmitted by the first RF device atvarious distances is a voltage signal with constant amplitude andcorresponding to the distance. FIG. 39 illustrates detection voltagesignal detected by the second device for directly-transmitted basebandsignal without modulation and the voltage waveform diagram of thedetected voltage signal for a sine-wave FSK modulation. In FIG. 39,39(a) is the voltage waveform diagram of the received voltage signal fordirectly-transmitted baseband signal without modulation, and 39(b) avoltage waveform diagram of the received voltage signal for a sine-waveFSK modulation. As shown in FIG. 39, the detection voltage signal is avariable voltage signal containing demodulation information. The signalmay be an AC voltage signal without any DC component, or may be avoltage signal having a DC component. The constant amplitude means thatthe maximum amplitude of the AC component in different transmissionsymbols keeps constant

The modulation mode, coding mode, and transmission magnetic flux densityBr of the first transmission parameters may be selected through thefollowing Step a41 to Step a43.

Step a41, selecting any coding mode without an average DC component,such as Manchester, Differential Manchester, NRZ, etc.

Step a42, selecting no modulation or a carrier modulation mode withoutamplitude change. The carrier modulation mode can use any modulationmethod without amplitude change. For example, the carrier wave may be asine wave carrier, a pulse carrier, or a triangle wave carrier, etc. Themodulation may be on-off keying (OOK), phase shift keying or frequencyshift keying (FSK), etc. In the no-modulation mode, the encoded basebandsignal is directly driven by the driver circuit and transmitted by thetransmitter coil.

Step a43, selecting the transmission magnetic flux density Br.Specifically, under a selected operating frequency that is less than f0,a selected modulation scheme and a selected coding mode, first selectingthe typical mobile terminal and the magnetic detection and theamplification gain that are easy to achieve by the second RF deviceinside the mobile terminal, then detecting inherent noise voltageamplitude Vn of the detection voltage of the second RF device when thefirst RF device is not sending the low-frequency alternating magneticfield signal. Further, detecting the detection voltage Vc of the secondRF device when the first RF device is sending the low-frequencyalternating magnetic field signal using the selected modulation andcoding scheme, and selecting the transmission magnetic flux density Brsuch that such that Vc/Vn>SNR, where SNR is the signal-to-noise-ratio ofthe second RF device. In general SNR value may be selected as large aspossible, as not to cause the transmission power of the second RF deviceto be too high. For example, the SNR may be selected as SNR=10. Afterthe SNR is determined, Br is also determined as described above.

Step b4, the second RF device detects the first low-frequencyalternating magnetic field signal.

More specifically, the second RF device receives and detects the firstlow-frequency alternating magnetic field signal sent by the first RFdevice at each distance through the first low-frequency channel, andamplifies the first low-frequency alternating magnetic field signal intoan electrical signal corresponding to the distance and with constantamplitude. Further, based on a preset threshold value, it can bedetermined whether the terminal with the second RF device enters intothe effective card transaction range. The threshold value may be set thesame for all terminals with the second RF device.

If the first low-frequency alternating magnetic field signal isamplified into a voltage signal corresponding to the distance and withconstant amplitude, the corresponding threshold value is a voltagethreshold value. The preset voltage threshold Vt can be set through thefollowing Step 601 to Step 603.

Step 601, under the selected transmission parameters, measuring thevoltage-distance curve obtained from various typical terminals andobstacles. The transmission parameters include frequency of thelow-frequency alternating magnetic field signal, modulation mode, codingmode, and transmission magnetic flux density Br, etc.

Step 602, obtaining a reference voltage-distance curve, the referencevoltage-distance curve is the middle value of the curves of the typicalterminals and obstacles, the voltage magnitude from the upper boundaryand the lower boundary of the curves the typical terminals and obstaclesis δ_(T)/2, as shown in FIG. 40.

Step 603, selecting the threshold value Vt of the detection voltage ofthe second RF device: the voltage value at the point (Din+Dv/2) on thereference voltage-distance curve is Vt.

When the voltage signal corresponding to the received firstlow-frequency alternating magnetic field signal is greater than or equalto the preset voltage threshold Vt, it can be determined that theterminal equipped with the second RF device enters the effective cardtransaction range.

Step c4, the second RF device transmits a second low-frequencyalternating magnetic field signal.

Specifically, if the voltage signal corresponding to the received firstlow-frequency alternating magnetic field signal is greater than or equalto the preset voltage threshold Vt, the terminal with the second RFdevice enters the effective card transaction range, the second RF deviceobtains the identification information of the first RF device from thereceived first low-frequency alternating magnetic field signal and,based on the second transmission parameters, transmits the secondlow-frequency alternating magnetic field signal through the secondlow-frequency channel. The second low-frequency alternating magneticfield signal carries the identification information of the first RFdevice obtained by the second RF device, and the identificationinformation of the second RF device itself. The second transmissionparameters include the frequency of the second low-frequency alternatingmagnetic field signal. This frequency is equal to or less than themaximum operating frequency f0′ of the system's second low-frequencychannel, and f0′ is the maximum operating frequency satisfying thetarget communication distance of Din˜Din+Dv′.

Before selecting the communication frequency f′ of the secondlow-frequency channel, it needs to determine that, under the secondlow-frequency channel communication mode, the change patterns of thevoltage-distance curves of all the typical terminal and obstaclesdetected by the first RF device, and the change patterns of voltage withrespect to change of the frequency.

FIG. 41 is a block diagram of a system for detecting thevoltage-distance curves under the second low-frequency channelcommunication mode. As shown in FIG. 41, the selection system comprises:a transmission system containing a signal source 091 and various typicalmobile terminals 092 (including transmitter coil 093 and variousobstacles), a receiving system containing low-frequency receiving module094 (including low-frequency receiver coil 095 and low-frequencyreceiving circuit 096), and a signal strength detector 097 (a voltmeter,an oscilloscope, a spectrometer, etc.).

The principle of detecting voltage and distance curve (voltage-distancecurve) includes: the signal source 091 generates a sine wave signal witha fixed amplitude and of frequency f′, which is transmitted by thetransmitter coil 093 in the mobile terminal 092, and the signal passesthrough or is diffracted through the typical mobile terminal andobstacles. The low-frequency receiver module 094 converts the receivedlow-frequency signal and passes the signal to the signal strengthdetector 097 through a dedicated signal line, and the signal strengthdetector 097 detects the received voltage. By changing the distance ofthe mobile terminal, the low-frequency receiving module receivescorresponding signals from the mobile terminal and obstacles, and thecurve of the detection voltage changes with the distance can beobtained, i.e., the voltage-distance curve, under the frequency f′. Themobile terminal and obstacles can be changed to obtain curves ofdifferent mobile terminals, and the frequency f′ can also be changed toobtain different curves.

FIG. 42 shows the voltage-distance curves detected by the system in FIG.41. As shown in FIG. 42, under the second low-frequency channelcommunication mode, the voltage-distance curves have similar patterns tothose under the first low-frequency channel communication mode, thevoltage detected by the first RF device decreases monotonically with thedistance.

When the frequency of the second low-frequency magnetic field signal isless than or equal to the frequency f0′, different mobile terminalsequipped with the second RF device are within the valid communicationdistance range, and no calibration is needed. The maximum operatingfrequency f0′ of the second low-frequency channel can determine by thefollowing steps.

Step 701, determining the system distance control target (Din, Dv′)based on the second low-frequency alternating magnetic field signal,where Din means that all terminals (with the second RF device) withinthe range of 0-Din are ensured for card transaction, and Dv′ denotes thedistance fluctuation range of the second low-frequency channel. If thedistance is within Din˜(Din+Dv′), card transactions are allowed and, ifthe distance is greater than Din+Dv, card transactions are not allowed.

Step 702, determining the fluctuation range δ_(R)′ of the detectionvoltage in the first RF device that is caused by the second RF device.

Step 703, determining the fluctuation range δ_(C)′ of the detectionvoltage caused by the first RF device itself.

Step 704, determining the voltage-distance curves of various typicalterminals and obstacles at the frequency f′.

Step 705, based on the distance control target (Din, Dv′), determiningfluctuation range δ_(A)′ of the detection voltage by the first RFdevice. The range δ_(A)′ equals to the difference between the voltagecorresponding to the point Din on the voltage-distance curve withaverage field intensity attenuation curve slope and obtained from thevoltage-distance curves of various typical terminals and obstacles andthe voltage corresponding to the point (Din+Dv′).

FIG. 43 illustrates the total received detection voltage fluctuationrange δ_(A)′ determined by the distance control target (Din, Dv) for thesecond low-frequency channel. As shown in FIG. 44, the point Dincorresponds to voltage value VP, and the point (Din+Dv′) corresponds tothe voltage value V2′, and δ_(A)′=V1′−V2′.

Step 706, determining the fluctuation range δ_(T)′ of the detectionvoltage of the second RF device caused by the mobile terminal. Theparameter δ_(T)′ represents the fluctuation range of the detectionvoltage of the second RF device caused by the attenuationcharacteristics of the terminal, δ_(T)′=δ_(A)′−δ_(R)′−δ_(C)′.

FIG. 44 illustrates a voltage-distance curves and fluctuation range δ′of a typical terminal and obstacle for the second low-frequency channel.As shown in FIG. 44, the voltage-distance curve corresponding to themaximum attenuation terminal and obstacle is called the maximumattenuation curve, and voltage-distance curve corresponding to theminimum attenuation terminal and obstacle is called the minimumattenuation curve. The area surrounded by the maximum attenuation curveand the minimum attenuation curve is called the voltage-distance curvedistribution area of the typical terminal and obstacle. Provided thatthe voltage corresponding to any D on the minimum attenuation curve isV3′, and the voltage corresponding to any D on the maximum attenuationcurve is V4′, then δ′=V3′−V4′.

Step 707, calculating the maximum field intensity difference δ′ atvarious distances with the distance control range of various typicalterminals and obstacles. If δ′ is greater than δ_(A)′, the frequency f′is decreased and the method goes to Step 704. If δ′ is less than δ_(T)′,the frequency f′ is increased and the method goes to Step 704. Further,if δ′ is equal to δ_(A)′, the current frequency f′ is equal to thefrequency f0′.

Thus, the maximum value f0′ of the communication frequency f′ of thesystem's second low-frequency channel can be determined. Within thefrequency range of less than the maximum value f0′, it can be ensuredthat the communication distance range of the second low-frequencychannel is within the range of Din˜Din+Dv′.

In one embodiment, the selection of the communication frequency f′ ofthe second low-frequency channel may also need to take intoconsideration of the interference of environmental noise, especiallyaudio noise.

Further, the second transmission parameters of the second RF device alsoinclude the low-frequency coding mode, modulation mode, andlow-frequency transmission magnetic flux density Bc. The transmissionparameters may be determined through the following steps.

Step c41, selecting any coding mode without an average DC component,such as Manchester, Differential Manchester, NRZ, etc.

Step c42, selecting no modulation or a carrier modulation mode withoutamplitude change. The carrier modulation mode can use any modulationmethod without amplitude change. For example, the carrier wave may be asine wave carrier, a pulse carrier, or a triangle wave carrier, etc. Themodulation may be on-off keying (OOK), phase shift keying or frequencyshift keying (FSK), etc. In the no-modulation mode, the encoded basebandsignal is directly driven by the driver circuit and transmitted by thetransmitter coil.

Step c43, selecting the transmission magnetic flux density Bc of thesecond low-frequency channel. Specifically, under a selected operatingfrequency that is less than f0′, a selected modulation scheme and aselected coding mode, first selecting the typical noise terminal and themagnetic detection and the amplification gain that are easy to achieveby the first RF device; then detecting inherent noise voltage amplitudeVn′ of the detection voltage of the first RF device when the mobileterminal is not sending the low-frequency alternating magnetic fieldsignal. Further, detecting the detection voltage Vr of the first RFdevice when the mobile terminal is sending the low-frequency alternatingmagnetic field signal using the selected modulation and coding mode. Thetransmission magnetic flux density Bc is selected such that Vr/Vn′>SNR′,where SNR′ is the signal-noise-ratio of the low-frequency signal of thefirst RF device. In general SNR′ value may be selected as large aspossible, as not to cause the transmission power of the second RF deviceto be too high. For example, the SNR′ may be selected as SNR′=10. Afterthe SNR′ is determined, Bc is also determined as described above.

Step d4, the first RF device detects the second low-frequencyalternating magnetic field signal.

Specifically, after receiving the second low-frequency alternatingmagnetic field signal, the first RF device obtains the identificationinformation carried by the signal, and compares the identificationinformation of the first RF device in the second low-frequencyalternating magnetic field signal with its own identificationinformation. If they are the same, the first RF device combines its ownidentification information and the identification information of thesecond RF device, which can be used for the RF communication address andchannel parameters of the RF communication to conduct card transactionwith the terminal equipped with the second RF device.

Step e4, based on the first low-frequency alternating magnetic fieldsignal detected by the second RF device and the second low-frequencyalternating magnetic field signal detected by the first RF device, thedistance between the first RF device and the second RF device can bedetermined, such that the second RF device and the first RF device canexchange information within a preset distance range through the RFchannel.

Further, the following steps can be performed to determine, based on thefirst low-frequency alternating magnetic field signal detected by thesecond RF device and the second low-frequency alternating magnetic fieldsignal detected by the first RF device, the distance between the firstRF device and the second RF device.

The second RF device converts the first low-frequency alternatingmagnetic field signal into a first electrical signal.

The second RF device compares the first electrical signal with a presetfirst threshold value and, based on the comparison result, determineswhether the second RF device enters into a predetermined valid distancerange between the first RF device and the second RF device.

The first RF device demodulates the second low-frequency alternatingmagnetic field signal to obtain the identification information of thefirst RF device carried in the second low-frequency alternating magneticfield signal.

The first RF device compares the demodulated identification informationof the first RF device and stored its own identification informationand, based on the comparison result, determines whether the first RFdevice enters into a predetermined valid distance range between thesecond RF device and the first RF device.

When the second RF device enters into the predetermined valid distancerange between the first RF device and the second RF device, and thefirst RF device enters into the predetermined valid distance rangebetween the second RF device and the first RF device, it can bedetermined that the distance between the second RF device and the firstRF device is within the predetermined valid communication distancerange.

Further steps may also be included: the first RF device converts thesecond low-frequency alternating magnetic field signal into a secondelectrical signal, the first RF device compares the second electricalsignal with the preset second threshold value and, based on thecomparison result, determines whether the first RF device enters into apredetermined valid distance range between the second RF device and thefirst RF device.

The above disclosed communication methods use the low-frequency two-waymagnetic-field detection techniques to achieve secure communicationdistance control, without the need for terminal calibration.

Additionally, because the current required for the low-frequencytransmission magnetic field intensity of the low-frequency channel isdrawn from the mobile terminal, the current can be provided by themobile terminal usually is limited to, for example, a maximum of 50 mA,the communication distance of the low-frequency channel will not beexpanded too much even when the transmission parameters of the mobileterminal is tampered, and the effective communication distance can stillbe controlled within about Din˜Din+Dv′ range

Further, the frequency of the low-frequency alternating magnetic fieldsignal may be in the low frequency band, very-low frequency band, orultra-low frequency band. For example, the ultra-low frequency band maybe in a range of approximately 300 Hz˜3000 Hz, the very-low frequencyband may be in a range of approximately 3 KHz˜30 KHz, and the lowfrequency band may be in a range of approximately 30 KHz˜300 KHz. Incertain embodiments, the frequency of the low-frequency alternatingmagnetic field signal can be in a range of approximately 300 Hz˜50 KHz.For example, the frequency of the first low-frequency alternatingmagnetic field signal can be approximately 500 Hz, 1 KHz, 1.5 KHz, 2KHz, 2.5 KHz, 3 KHz, 4 KHz, 5 KHz, 10 KHz, 20 KHz, 30 KHz, 40 KHz or 50KHz; and the frequency of the second low-frequency alternating magneticfield signal can be approximately 10 KHz, 15 KHz, 20 KHz, 25 KHz or 30KHz.

According to the disclosed embodiments, a communication system is alsoprovided for using the low-frequency two-way magnetic-field detectiontechniques to achieve effective communication distance control,implementing the above disclosed methods.

FIG. 45 is a block diagram of an overall structure of a communicationsystem according to disclosed embodiments. As shown in FIG. 45, in thisembodiment, the communication system 2000 includes a first RF device2100 and a second RF device 2200. The first RF device 2100 and second RFdevice 2200 control the communication distance through the low-frequencyalternating magnetic field signals, and exchanges information throughthe RF channel.

Also shown in FIG. 45, the first RF device 2100 includes a firstmagnetic signal transceiver 2100 and a first RF communication unit 2120.The magnetic signal transceiver 2100 is configured to generate andtransmit the first low-frequency alternating magnetic field signal, andto receive the second low-frequency alternating magnetic field signal,and the first radio communication unit 2120 is configured to exchangeinformation with a second RF communication unit 2220. The second RFdevice 2200 includes a magnetic signal transceiver 2210 and the secondRF communication unit 2220. The magnetic signal transceiver 2210 isconfigured to generate and transmit the second low-frequency alternatingmagnetic field signal, and to receive the first low-frequencyalternating magnetic field signal. The second RF communication unit 2220is configured to exchange information with the first RF communicationunit 2120.

Of course, the first magnetic signal transceiver 2100 may furtherinclude a first magnetic signal receiving unit and a first magneticsignal transmitting unit (not shown). The first magnetic signaltransmitting unit is configured to transmit the first low-frequencyalternating magnetic field signal, and the first magnetic signalreceiving unit is configured to receive the second low-frequencyalternating magnetic field signal. The second magnetic signaltransceiver 2210 may further include a second magnetic signal receivingunit and a second magnetic signal transmitting unit (not shown). Thesecond magnetic signal transmitting unit is configured to transmit thesecond low-frequency alternating magnetic field signal, and the secondmagnetic signal receiving unit is configured to receive the firstlow-frequency alternating magnetic field signal.

FIG. 46 is a specific configuration of the first magnetic signaltransceiver 2100 and the second magnetic signal transceiver 2210. Asshown in FIG. 46, the first magnetic signal transceiver 2100 maycomprise a first modulation unit 2111, and the first modulation unit2111 is configured to add the identification information of the first RFdevice into the first low-frequency alternating magnetic field signal.The second magnetic signal transceiver 2210 may comprise a secondmodulation unit 2211, and the second modulation unit 2211 is configuredto add the identification information of the second RF device into thesecond low-frequency alternating magnetic field signal. Specifically,the first modulation unit 2111 can be included in the first magneticsignal transmitting unit of the first magnetic signal transceiver 2100,and the second modulation unit 2211 may be included in the secondmagnetic signal transmitting unit of the second magnetic signaltransceiver 2210.

Further, in FIG. 46, the first magnetic signal transceiver 2100 can alsoinclude a first determination unit 2112. The first determination unit2112 is configured to determine whether the first RF device enters intothe preset valid card transaction range between the second RF device andthe first RF device, based on the second low-frequency alternatingmagnetic field signal detected by the first RF device. Further, thesecond magnetic signal transceiver 2210 can also include a seconddetermination unit 2212. The second determination unit 2212 isconfigured to determine whether the second RF device enters into thepreset valid card transaction range between the first RF device and thesecond RF device, based on the first low-frequency alternating magneticfield signal detected by the second RF device. When the firstdetermination unit 2112 determines that the first RF device enters intothe preset valid card transaction range between the second RF device andthe first RF device, and the second determination unit 2212 determinesthat the second RF device enters into the preset valid card transactionrange between the first RF device and the second RF device, it can bedetermined that the distance between the first RF device and the secondRF device is within the predetermined effective communication distancerange. Specifically, the first determination unit 2112 can be includedin the first magnetic signal receiving unit of the first magnetic signaltransceiver 2100, and the second determination unit 2212 may be includedin the second magnetic signal receiving unit of the second magneticsignal transceiver 2210.

Of course, the first magnetic signal transceiver 2100 and/or the secondmagnetic signal transceiver 2210 may further include a magnetic signalreceiving unit (not shown), a magnetic signal transmitting unit (notshown) and the like, the detailed descriptions of which are omittedherein.

FIG. 47 illustrates a specific configuration of the first determinationunit 2112 and the second determination unit 2212 shown in FIG. 46. Asshown in FIG. 47, the first determination unit 2112 may comprise a firstcomparison sub-unit 21121 and a first determination sub-unit 21122. Thefirst comparison sub-unit 21121 is configured to compare theidentification information of the first RF device demodulated from thesecond low-frequency alternating magnetic field signal with its ownstored identification information; and the first determination sub-unit21122 is configured to, based on the comparison result, determineswhether the first RF device enters into a predetermined valid distancerange between the second RF device and the first RF device.

The second determination unit 2212 can include a second comparisonsub-unit 22121 and a second determination sub-unit 22122. The secondcomparison sub-unit 22121 is configured to compare the electrical signalconverted from the first low-frequency alternating magnetic field signalwith the preset threshold value, and the second determination sub-unit22122 is configured to, based on the comparison result, determineswhether the second RF device enters into a predetermined valid distancerange between the second RF device and the first RF device.

It should be noted that, those skilled in the art can understand thatthe multiple modules or units may be combined into one module or unit,and one module or unit can be further divided into multiple sub-modulesor sub-units.

According to the disclosed embodiments, the communication systemcomprises at least one first RF device and at least one second RFdevice. The first RF device and the second RF device performcommunication distance control through low-frequency alternatingmagnetic field signals, and the first RF device and the second RF deviceexchange information via the RF channel. Further, the first RF deviceincludes a first magnetic signal transceiver configured to generate andtransmit the first low-frequency alternating magnetic field signal andto receive the second low-frequency alternating magnetic field signal,and a first radio communication unit configured to exchange informationwith a second RF communication unit. The second RF device includes asecond magnetic signal transceiver configured to generate and transmitthe second low-frequency alternating magnetic field signal, and toreceive the first low-frequency alternating magnetic field signal, and asecond RF communication unit configured to exchange information with thefirst RF communication unit.

Specifically, the first RF device can transmit the first low-frequencyalternating magnetic field signal based on the first transmissionparameters through the first low-frequency channel. The firstlow-frequency alternating magnetic field signal carries theidentification information of the first RF device, and the firsttransmission parameters can include the frequency of the firstlow-frequency alternating magnetic field signal. This frequency is lessthan or equal to the highest frequency f0′ of the first low-frequencychannel. The first RF device can also receive the second low-frequencyalternating magnetic field signal transmitted by the second RF devicebased on the second transmission parameters through the secondlow-frequency channel, and compare identification information of thefirst RF device carried in the second low-frequency alternating magneticfield signal with its own identification information. If they are thesame, the first RF device combines its own identification informationand the identification information of the second RF device, which can beused for the RF communication address and channel parameters of the RFcommunication to conduct card transaction with the terminal equippedwith the second RF device through the RF channel.

More specifically, the second RF device receives and detects the firstlow-frequency alternating magnetic field signal sent by the first RFdevice at each distance through the first low-frequency channel, andamplifies the first low-frequency alternating magnetic field signal intoan electrical signal corresponding to the distance and with constantamplitude (a voltage signal or a current signal). Further, based on apreset threshold value, it can be determined whether the terminal withthe second RF device enters into the effective card transaction range.The threshold value may be set the same for all terminal with the secondRF device

When the voltage signal corresponding to the received firstlow-frequency alternating magnetic field signal is greater than or equalto the preset voltage threshold, the second RF device obtains theidentification information of the first RF device from the receivedfirst low-frequency alternating magnetic field signal and, based on thesecond transmission parameters, transmits the second low-frequencyalternating magnetic field signal through the second low-frequencychannel. The second low-frequency alternating magnetic field signalcarries the identification information of the first RF device obtainedby the second RF device, and the identification information of thesecond RF device itself. The second transmission parameters include thefrequency of the second low-frequency alternating magnetic field signal.This frequency is equal to or less than the maximum operating frequencyf0′ of the second low-frequency channel. The second RF device can thenconduct card transactions with the first RF device through the RFchannel.

FIG. 48 shows an exemplary communication system according to disclosedembodiments. As shown in FIG. 48, the communication system consists oftwo parts: the first RF device 3000 and the second RF device 4000.

The first RF device 3000 may comprise at least one transmitter coil3006, at least one driver circuit 3005, at least an encoding circuit3003, and at least a first main processor 3002. The low-frequencytransmitter coil 3006, the driver circuit 3005, the encoding circuit3003 and the first main processor 3002 are sequentially connected inseries. The first RF device 3000 may also comprise at least alow-frequency magnetic induction circuit 3007, at least onelow-frequency amplifier and filter circuit 3008, at least a demodulationcircuit 3009. The low-frequency magnetic induction circuit 3007, thelow-frequency amplifier and filter circuit 3008, and the demodulationcircuit 3009 are sequentially connected to the first main processor 3002in series. Further, the first RF device 3000 may at least one RFtransceiver circuit 3011 and an RF antenna 3010. The RF antenna 3010 andthe RF transceiver circuit 3011 are sequentially connected to the firstmain processor 3002 in series. There may be a modulation circuit 3004provided between the drive circuit 3005 and the encoding circuit 3003,and the drive circuit 3005, the modulation circuit 3004, and theencoding circuit 3003 may be sequentially connected in series.

The second RF device 4000 may comprise at least one transmitter coil4006, at least one driver circuit 4005, at least an encoding circuit4003, and at least a second main processor 4002. The low-frequencytransmitter coil 4006, the driver circuit 4005, the encoding circuit4003 and the second main processor 4002 are sequentially connected inseries. The second RF device 4000 may also comprise at least alow-frequency magnetic induction circuit 4007, at least onelow-frequency amplifier and filter circuit 4008, at least a thresholdjudgment and demodulation circuit 4009. The low-frequency magneticinduction circuit 4007, the low-frequency amplifier and filter circuit4008, and the threshold judgment and demodulation circuit 4009 aresequentially connected to the second main processor 4002 in series.Further, the second RF device 4000 may at least one RF transceivercircuit 4011 and an RF antenna 4010. The RF antenna 4010 and the RFtransceiver circuit 4011 are sequentially connected to the second mainprocessor 4002 in series. There may be a modulation circuit 4004provided between the drive circuit 4005 and the encoding circuit 4003,and the drive circuit 4005, the modulation circuit 4004, and theencoding circuit 4003 may be sequentially connected in series.

In certain circuitry implementation, the low-frequency transmitter coilor coils can be wire coil or PCB coil. Preferably, the low-frequencytransmitter coil can have more than 4 turns.

Preferably, the low-frequency transmitter coil of the first RF devicecan be filled with a ferrite core or an iron core. The largest width ofthe cross-sectional area enclosed by the low-frequency transmit coil ofthe first RF device may be greater than the width of the cross-sectionalarea of the second RF device. Preferably, the cross-sectional areaenclosed by the low-frequency transmit coil of the first RF device mayinclude at least a circular cross-sectional area with a diameter of 3 cmor a square area of 3 cm×3 cm. Preferably, the low-frequency transmittercoil of the first RF device can have approximately 50 to 500 turns.

The magnetic induction device used by the low-frequency magneticinduction circuit may be a wire coil, a PCB coil, a Hall device or agiant magnetoresistive device. Preferably, the low-frequency magneticinduction circuit of the first RF device is a low-frequency receivercoil, and the low-frequency receiver coil can have approximately 50 to500 turns.

Further, the second RF device may be disposed inside a mobile terminalor on a SIM card, a UIM card, a USIM card, a TF card, or an SD card inthe mobile terminal. The mobile terminal may include a mobile phone, apersonal digital assistant PDA, an MP4 or a laptop computer, etc.

The implementation of the communication system is illustrated asfollows.

(1), The communication frequency f of the first low-frequency channeland the communication frequency f′ of the second low-frequency channelcan be selected using previously-describe methods, the details of whichare not repeated herein.

(2), the Process for Distance Control and Connection the Second RFDevice to the First RF Device.

The first RF device switches back and forth between a low-frequencytransmitting state and a low-frequency receiving state at a fixedperiod. When in the transmitting state, the first RF device transmitsthe first low-frequency alternating magnetic field signal at a frequencyno higher than the selected frequency f0 using preconfiguredtransmission parameters and based on the distance control target. Thefirst low-frequency alternating magnetic field signal carries a dataframe based on modulated signal or direct baseband signal. The dataframe contains a unique identifier IDr of the first RF device (of coursecan also be other identification information). When the mobile terminalwith the second RF device is placed around the first RF device, thelow-frequency alternating magnetic field signal penetrates the mobileterminal and reaches the second RF device. The second RF device detectsand amplifies the low-frequency alternating magnetic field signal ateach distance point into a voltage signal of constant amplitude andcorresponding to the distance point.

When the voltage value is lower than the preset threshold value Vt inthe second RF device, it indicates that the terminal does not enter intoa valid card transaction range, and card transactions are not allowed.When the voltage amplitude is higher than the preset voltage thresholdVt, it indicates that the terminal enters into the valid cardtransaction range of the first RF device, and the second RF deviceparses the information in the magnetic field signal and obtains theidentifier IDr of the first RF device. The second RF device then sendsthe second low-frequency alternating magnetic field signal to the firstRF device, and the signal carries a data frame based on modulated signalor direct baseband signal. The data frame contains the unique identifierIDr of the first RF device and a unique identifier IDc of the second RFdevice. The first RF device parses the magnetic field signal and obtainsthe IDr and the IDc, and compares with the received IDr and its own IDr.If the received IDr is the same as its own IDr, it indicates that thefirst RF device and the terminal enter into the valid card transactionrange. The first RF device combines the IDr and the IDc to generate theRF communication address and initiate card transaction. Further, when acard transaction is initiated, the first RF device is no longerswitching between the low-frequency transmitting state and thelow-frequency receiving state periodically. Instead, the first RF devicecontinuously transmits the low-frequency magnetic field signal to ensurethat the mobile terminal with the second RF device and the first RFdevice are always within the valid card transaction range. Thus, thesecond RF device and the first RF device can be uniquely bond, with bothsides using the unique combined address (IDr, IDc) to identify eachother. After the binding, the communication process for data exchangeusing the RF channel is less likely to generate errors. That is, afterthe second RF device is successfully bond with or connected to the firstRF device, the distance control process is completed, and a subsequentcard transaction can be carried out on the RF channel until the end ofthe transaction.

(3), the Transaction Process.

The first RF device and the second RF device establish the unique andreliable communication link through the RF channel. Based on thecommunication link, the two sides can complete the authenticationrequired by the transaction and other processes required by thetransaction. All of these processes can be accomplished by a fast RFchannel. Because the above described process can ensure that theconnection can only be made within a predetermined distance range, theentire transaction process can also be communication limited within thepredetermined distance range.

Further referring to FIG. 48, the communication system consists of twoparts: the first RF device 3000 and the second RF device 4000. Thesecond RF device 4000 is placed inside a mobile terminal and interactswith the mobile terminal through terminal communication interfaces.

The first RF device 3000 may comprise the following modules: a firstmain processor 3002, responsible for the first RF device low frequencyand high frequency control and processing other protocols, the firstmain processor 3002 can connect to the external communication interfacevia the interface circuit 3001 or directly; an encoding circuit 3003responsible for coding the low-frequency frame data bit by bit; amodulation circuit 3004 responsible for modulating the symbol streamoutputted by the encoding circuit against a carrier wave to generate amodulated signal to the drive circuit 3005 or for directly sending theencoded signal to the drive circuit 3005 if no modulation is used; adrive circuit 3005, responsible for driving the low-frequencytransmitter coil 3006 to generate the low-frequency alternating magneticfield signal 5000; a low-frequency magnetic induction circuit 3007comprising a PCB coil, a wire coil, a giant magnetoresistive device, aHall device, or other circuit elements capable of sensing magnetic fieldchanges, responsible for inducing and converting the low-frequencyalternating magnetic field signal 6000 into an electrical signal; alow-frequency amplifier and filter circuit 3008 responsible foramplifying the electrical signal detected by the low-frequency magneticinduction circuit and filtering out the noise component; a demodulationcircuit 3009 responsible for demodulating the low-frequency signal withthe noise component filtered out to generate the encoded signaltransmitted by the encoding circuit 4003 of the second RF device 4000,and sending the demodulated encoded signal to the first main processor3002. The first main processor 402 is responsible for decodingprocessing. An RF transceiver circuit 3011 is responsible for completingRF two-way communication with the RF transceiver module of the second RFdevice 4000 through the RF antenna 3010.

The second RF device 4000 may comprise the following modules: a secondmain processor 4002 responsible for controlling low-frequency and RFmodules and processing other protocols and also responsible forcommunicating with the mobile terminal; an SIM/TF/SD card module 4001being internal SIM/TF/SD card module of the mobile terminal, the moduletype is determined by the specific type of the card; a low-frequencymagnetic induction circuit 4007 comprising a PCB coil, a wire coil, agiant magnetoresistive device, a Hall device, or other circuit elementscapable of sensing magnetic field changes, responsible for inducing andconverting the low-frequency alternating magnetic field signal 5000 intoan electrical signal; a low-frequency amplifier and filter circuit 4008responsible for amplifying the electrical signal detected by thelow-frequency magnetic induction circuit into a low-frequency detectionvoltage signal; a threshold judgment and demodulation circuit 4009responsible for comparing the value of the low-frequency detectionvoltage signal the value with the preset threshold value Vt. If thevalue does not reach the threshold Vt, demodulation is not performed andany card transaction is not allowed. If the value reaches the presetthreshold value Vt, the demodulation is performed and the demodulatedsignal is sent to the second main processor 4002. The second RF device4000 also includes an encoding circuit 4003, responsible for encoding alow-frequency frame bit by bit; a modulation circuit 4004 responsiblefor modulating the symbol stream outputted by the encoding circuitagainst a carrier wave to generate a demodulated signal to the drivecircuit 4005 or for directly sending the encoded signal to the drivecircuit 4005 if no modulation is used; the drive circuit 4005,responsible for driving the low-frequency transmitter coil 4006 togenerate the low-frequency alternating magnetic field signal 6000; andan RF transceiver circuit 4011 responsible for completing RF two-waycommunication with the RF transceiver module of the first RF device 3000through the RF antenna 4010.

The communication system achieves distance detection and control withoutcalibration by determining the low-frequency communication thresholdfrom the first RF device to the mobile terminal and the low-frequencycommunication distance limitation from the mobile terminal to the RFcard reader. That is, the first RF device 3000 transmits the firstlow-frequency alternating magnetic field signal 5000 in accordance withthe preset transmission parameters, and the second RF device 4000receives the magnetic field signal and converts it into a low-frequencydetection voltage signal, and uses a preset threshold value to determinewhether the terminal enters the preset valid distance range set by thefirst RF device 3000. After entering the valid distance range, thesecond RF device 4000 transmits the second low-frequency alternatingmagnetic field signal 6000 to the first RF device 3000. The first RFdevice 3000 receives the magnetic field signal and analyzes the data inthe received signal. If the data is legitimate, it indicates that thefirst RF device 3000 and the mobile terminal enter into the valid cardtransaction range set by the system. Thus, the unique binding betweenthe first RF device 3000 and the second RF device 4000 is realized byusing the combination of the two-way low-frequency communication andtwo-way RF communication. That is, the first RF device 3000 uses thefirst low-frequency channel to send its unique identification IDr to thesecond RF device 4000, and the second RF device 4000 uses the secondlow-frequency channel to send its unique identification IDc appended tothe identification IDr to the first RF device 3000. The first RF device3000 determines the correctness returned IDr, and achieves a uniquebinding between the second RF device 4000 and the first RF device 3000.After the binding, the RF channel can be used to perform two-wayhigh-speed communication of large amount of data.

The specific workflow of the communication system are illustrates in thefollowings.

(A) First, basic operation parameters of the system are selected,including the RF frequency, first low-frequency channel communicationfrequency f, second low-frequency channel communication frequency f′,first RF device transmission parameters, second RF device transmissionparameters, second RF device receiving voltage threshold Vt, and firstRF device receiving circuitry parameters, etc.

1. Selecting the RF Frequency

The RF communication frequency may be selected above 2400˜2483 MH 2.4GISM band, so as to achieve high-speed communication and good terminalpenetration. Other frequency, such as 433 MHz, 900 MHz, 5 GHz, or thelike, can also be used.

2. Selecting the Communication Frequency f of the First Low-FrequencyChannel

The method described above can be used to determine the communicationfrequency f of the first low-frequency channel. For a typical GSM mobileterminal, to achieve a range of 0˜10 cm distance control, the frequencyf0 may be less than 10 KHZ, such as such as 500 HZ, 1 KNZ, 1.5 KHZ, 2KHZ, 2.5 KHZ, 3 KHZ, or 5 KHZ, etc.

3. Selecting the Communication Frequency f′ of the Second Low-FrequencyChannel

The method described above can be used to determine the communicationfrequency f′ of the second low-frequency channel, with consideration onnoise interference especially the audio interference. The frequency f′may be selected between 20 KHZ and 50 KHz, such as 30 KHZ, 40 KHZ, or 50KHZ, etc.

4. Selecting the First RF Device Transmission Parameters.

The transmission parameters include modulation mode, coding scheme andtransmission magnetic induction intensity Br.

FIG. 49 is a schematic diagram of the low-frequency transmitter part ofthe first RF device. As shown in FIG. 49, the low-frequency transmitterportion of the first RF device includes a low-frequency transmittercircuit and a low-frequency transmitter coil. Referring to FIG. 48, thelow-frequency transmitter circuit of the first RF device comprises thedriving circuit 3005, the modulation circuit 3004, and the encodingcircuit 3003. The low-frequency modulated signal driven by the drivingcircuit 3005 is outputted to the low-frequency transmitter coil 3006.

The modulation circuit 3004 can use the following modulation schemes:

(1) Carrier modulation: the baseband signal generated by the encodingcircuit 3003 is modulated by the modulation circuit 3004 against thecarrier, and the carrier may be a sine wave, a square wave, or atriangular wave, etc. The modulation can use On-off frequency shiftkeying (OOK), phase shift keying, frequency shift keying (FSK), etc. Themodulated signal is loaded onto the low-frequency transmitter coil 3006through the driving circuit 3005.

(2) No-carrier direct baseband transmission: the baseband signalgenerated by the encoding circuit 3003 is loaded directly onto thelow-frequency transmitter coil 3006 through the drive circuit 3005.

(3) Other modulations: because the distance control is based on thethreshold, the modulation mode used in general less prefers amplitudemodulation, other modulation schemes that can maintain the detectionvoltage amplitude of the RF card substantially constant can also beused.

Encoding circuit 3003 can use the following encoding schemes:

(1) Manchester encoding: 1 bit is encoded as two symbols 01, bit 0 isencoded as 10.

(2) Differential Manchester encoding: two bit symbol sequences, 01 and10, bit 1 is encoded differently from the previous symbol sequence, andbit 0 is encoded the same, or vice versa.

(3) Other encoding schemes: because the distance control is based on thethreshold, the encoding may need to keep the average value of thelow-frequency modulated signal, and the encoded sequence does notcontain a DC component. Any encoding scheme resulting in zero average DCcomponent can be used.

After selecting the modulation and coding schemes, the transmissionmagnetic induction intensity Br of the first RF device can be determinedusing the method described previously. The parameter Br can be adjustedby adjusting turns, diameter, and/or shape of the coil.

5. Selecting the Second RF Device Receiving Voltage Threshold Vt

The second RF device receiving voltage threshold Vt can be selectedusing the method described previously.

6. Selecting the Second RF Device Transmission Parameters

Referring to FIG. 48, the low-frequency transmitter circuit of thesecond RF device includes the driving circuit 4005, the modulationcircuit 4004, and the encoding circuit 4003. The low-frequency modulatedsignal driven by the driving circuit 4005 is outputted to thelow-frequency transmitter coil 4006.

Preferably, the modulation circuit 4004 can use the carrier modulationformat. The encoding circuit 4003 can use various encoding modes, suchas Manchester, Differential Manchester, NRZ, etc.

After selecting the modulation and coding schemes, the transmissionmagnetic induction intensity Bc of the second RF device can bedetermined using the method described previously. The parameter Bc canbe adjusted by adjusting turns, diameter, and/or shape of the coil, andgain parameters of the driving circuit 4005.

7. Selecting the First RF Device Low-Frequency Receiving CircuitryParameters

Referring to FIG. 48, the first RF device low-frequency magneticinduction circuit 3007 includes a winding-wire coil, a PCB coil, a Halldevice, or a giant magnetoresistance device. Any such device withdesired sensitivity can be selected in the low-frequency magneticinduction circuit of the first RF device.

The above parameters may only need to be selected once. After they areselected, no change might be required during operation.

(B) Second, the system operational flow after determining the operationparameters:

Step A701: distance detection and control process. The first mainprocessor 3002 of the first RF device 3000 generates a data framecontaining a unique identifier IDr of the first RF device 3000 and sendsit to the encoding circuit 3003 to be encoded. The encoded signal ismodulated by the modulation circuit 3004 and passed to the drive circuit3005 or is directly passed to the drive circuit 3005 without modulation,the modulated voltage is sent to the low-frequency transmitter coil3006. Based on preconfigured frame format, modulation and codingschemes, and driving capability, the transmitter coil 3006 transmits thefirst low-frequency alternating magnetic field signal 301 at the presetintensity Br periodically in accordance with the selected frame formatand transmission parameters.

When the mobile terminal is placed around the first RF device 3000, thefirst low-frequency alternating magnetic field signal 3001 penetratesthe terminal and reaches the low-frequency detection end of the secondRF device 4000. The low-frequency magnetic induction circuit 4007 of thesecond RF device 4000 detects and amplifies the first low-frequencyalternating magnetic field signal into an electrical signal. Theelectrical signal is amplified and filtered out noise component by thelow-frequency amplifier circuit 4007 to generate a low-frequencydetection voltage. When the voltage amplitude is less than the presetthreshold value Vt, card transactions are not allowed. When voltageamplitude is greater than or equal to the preset threshold value Vt, itindicates that the terminal enters into the predetermined effectivecommunication distance range of the first RF device, the thresholdjudgment and demodulation circuit 4009 parses the voltage signal toobtain IDr and send it to the second main processor 4002.

The second main processor 4002 combines the unique identifier IDc of thesecond RF device and the unique identifier IDr of the first RF deviceinto a data frame and sends it to the encoding circuit 4003. The encodedsignal is modulated by the modulation circuit 4004 and passed to thedrive circuit 4005 or is directly passed to the drive circuit 4005without modulation, the modulated voltage is sent to the low-frequencytransmitter coil 4006. Based on preconfigured frame format, modulationand coding schemes, and preset magnetic field intensity Bc, thetransmitter coil 4006 transmits the low-frequency alternating magneticfield signal 6000 periodically in accordance with the selectedparameters.

The low-frequency magnetic induction circuit 3007 of the first RF devicedetects the low-frequency magnetic field signal and converts it into anelectrical signal. The electrical signal is amplified and filtered outnoise component by the low-frequency amplifier circuit 3008 to generatea low-frequency detection voltage. The voltage signal is processed bythe low-frequency demodulation circuit 3009 to obtain the originalencoded signal sent by the second RF device, which is then sent to thefirst main processor for decoding processing. After decoding, the IDrand the IDc is obtained, the first main processor determines whether thereceived IDr and its own IDr are the same. If the received IDr and itsown IDr are not the same, card transactions are not allowed. If thereceived IDr and its own IDr are the same, it indicates that the firstRF device and the mobile terminal enter into the preconfigured validcard transaction range.

The frame format in Step A701 can be defined as follows:

FIG. 50 illustrates a low-frequency data frame transmitted by the firstRF device. As shown in FIG. 50, the first RF device low-frequency dataframe includes the following.

Preamble: 8 bits, usually FFH, for frame synchronization.

Control field: eight bits, providing information for reading the frame,such as length, data type, etc., reserved bits can used for expansion.

IDr: N bits, the unique identifier of the first RF device, specified bythe control field, where N is a natural number.

CRC: the checksum for the control field and the IDr, CRC checksum orother format can be used.

FIG. 51 illustrates a low-frequency data frame transmitted by the secondRF device. As shown in FIG. 51, the second RF device low-frequency dataframe includes the following.

Preamble: 8 bits, usually FFH, for frame synchronization.

Control field: eight bits, providing information for reading the frame,such as length, data type, etc., reserved bits can used for expansion.

IDr+IDc: N bits, the unique identifier of the first RF device and theunique identifier of the second RF device, specified by the controlfield, where N is a natural number.

CRC: the checksum for the control field, the IDr, and the IDc, CRCchecksum or other format can be used.

The above-described frame format is only an example, any frame formatcontaining the unique identifier of the RF card or the card reader canbe used. The unique identifier can be a random number of sufficientlength, the card reader may also be manually assigned a unique code, orother methods may be used to generate the unique identifier.

Step A702: as described in Step A701, after the first RF devicedetermines that the received IDr information and its own IDr informationare consistent, it indicates that the first RF device and the second RFdevice enter a valid card transaction range preconfigured by the system.The first main processor 4002 set the combination of the IDr and IDc asthe RF communications address, so that the first RF device withidentification IDc and the first RF device with identification IDr canestablish unique communication. Thus, the second RF device and the firstRF device are uniquely bond together, using the combination address(IDr, IDc) to uniquely identify each other. After the binding, thecommunication process over the RF channel is less likely to generateerrors. After the second RF device is successfully connected to or bondto the first RF device, the distance control process is completed, andthe subsequent card transaction process can be carried out on the RFchannel.

The unique identifier IDc of the second RF device in Step A702 can be aunique identifier pre-stored in the nonvolatile memory (NVM) of the RFcard, or a random number with a sufficient length internally generatedby the second RF device.

Step A703: transaction process.

The first RF device 3000 and the second RF device 4000 establish areliable and unique communication link through the RF channel. Based onthe link, the two sides can complete the authentication required by thetransaction and other processes required by the transaction. All ofthese processes can be accomplished by a fast RF channel. Because StepsA701˜A702 can ensure that the connection to the second RF device canonly be made within a predetermined distance range, the entiretransaction process can also be communication limited within thepredetermined distance range. The transaction process may be a POStransaction process, the details are omitted herein.

The low-frequency signal detection circuit 3007 and/or 4007 of the firstRF device 3000 and the second RF device 4000 may comprise a PCB coil, awire coil, a GMR device, or a Hall device. Other sensing device may alsobe used, so long as the device is capable of converting the magneticfield into an electrical signal, and with desired magnetic inductionsensitivity. Only limitation is that the low-frequency signal detectioncircuit 4007 of the second RF device 4000 needs to be placed internallyin a card, while the low-frequency signal detection circuit 3007 of thefirst RF device 3000 prefers magnetic induction components with highsensitivity.

Thus, the disclosed communication system can use low-frequencyalternating magnetic field to achieve distance detection and control,and to achieve two-way low-frequency communication between the first RFdevice and the second RF device. The RF channel can be used incombination with the low-frequency two-way communication to achievereliable and unique binding with the terminal, and the RF channel can beused to achieve high-speed data communication between the first RFdevice and the second RF device. Certain characteristics include: (1)the mobile terminal does not need to be modified, only needs to replacethe SIM/TF/SD card inside the mobile terminal and the reliable two-waydistance communication can be achieved; (2) because the current providedby the second RF device is limited, the communication distance of thelow-frequency signal is limited, which can prevent the transmissionpower of the second RF device being tampered or increased, and thecommunication distance can be effectively controlled within apredetermined range. In addition, the RF transceiver circuit is placedwithin the second RF device to achieve two-way high-speed communicationwith the RF transceiver circuit with the first RF device. Because theantenna of the RF circuit is very small, it can be easily integratedinto the SIM/TF/SD card.

According to the disclosed embodiments, the frequency f is selected tobe less than the frequency f0 and the frequency f′ is selected to beless than the frequency f0′, no calibration is needed when the systemoperates at these frequencies, and the communication distance can becontrolled safely and effectively. As an extension, frequency f may alsobe selected above the frequency f0 or frequency f′ may also be selectedabove the frequency f0′, which may cause reduced performance, reduceddistance control accuracy, and/or reduced communication success rate.However, such use does not conflict with the disclosed invention, andmerely an extension with modified performance.

According to the disclosed embodiments, two-way detection of alow-frequency alternating magnetic field signal can be used toeffectively control the communication distance, improving the problem ofuncontrollable communication distance and improving the security of cardtransaction communication and enhancing the security of card transactioncommunications.

The above mentioned examples are only some disclosed embodiments, andare not used to limit the present invention. Within the spirit and thescope of the present invention, any modifications, equal substitutionsand improvements of those embodiments are all within the scope of thepresent invention.

1. A communication method, comprising: controlling a communicationdistance between a first radio frequency (RF) device and a second RFdevice using a low-frequency magnetic field; and exchanging informationbetween the first RF device and the second RF device within apredetermined distance range using RF channels.
 2. The communicationmethod according to claim 1, wherein: one of the first RF device and thesecond RF device receives a first low-frequency alternating magneticfield signal from the other of the first RF device and the second RFdevice to control communication distance between the first RF device andthe second RF device.
 3. The communication method according to claim 2,wherein receiving the first low-frequency alternating magnetic signal tocontrol the communication distance further includes: detecting thereceived first low-frequency alternating magnetic field signal;converting the first low-frequency alternating magnetic field signalinto a first electrical signal; comparing the first electrical signalwith a first preset threshold value; and controlling the communicationdistance between the first RF device and second RF device based on acomparison result.
 4. (canceled)
 5. The communication method accordingto claim 4, wherein: the first RF device is a card reader, the second RFdevice is a card, the first electrical signal is a voltage signal, andthe first threshold value is a voltage threshold Vt, wherein the voltagethreshold Vt is determined by: under selected transmission parameters,measuring voltage-distance curves of a plurality of typical terminalsand obstacles, the selected transmission parameters including afrequency of the low-frequency alternating magnetic field signal, amodulation mode, a coding mode, and a transmission magnetic flux densityBc; and obtaining a reference voltage-distance curve, the referencevoltage-distance curve being a average value of curves of the typicalterminals and obstacles; and selecting a voltage value at a distancepoint at half of a maximum valid card transaction range on the referencevoltage-distance curve as Vt for the card reader.
 6. The communicationmethod according to claim 2, wherein: the first low-frequencyalternating magnetic field signal is related to a frequency f0 and, whena frequency of first low-frequency alternating magnetic field signal isless than or equal to the frequency f0, the first RF device and thesecond RF device are within a valid distance range.
 7. The communicationmethod according to claim 6, wherein the first RF device is a cardreader, the second RF device is a card, and the frequency f0 isdetermined by: determining a distance control target (Din, Dv) based onthe first low-frequency alternating magnetic field signal, wherein Dinrepresents a distance in which, within a range of 0-Din, cardtransaction is ensured, and Dv represents a distance fluctuation rangein which, within Din˜(Din+Dv), card transaction is allowed and, beyondDin+Dv, card transaction is not allowed; determining a detection voltagefluctuation range δ_(R) of the card reader; determining a detectionvoltage fluctuation range δ_(C) of the card; determiningvoltage-distance curves of the plurality typical terminals and obstaclesat the frequency f of first low-frequency alternating magnetic fieldsignal; based on the distance control target (Din, Dv), determining adetection voltage fluctuation range δ_(A) of the card reader, the rangeδ_(A) being equal to a difference between a voltage corresponding to adistance point Din on a voltage-distance curve with an average fieldintensity attenuation curve slope and obtained from the voltage-distancecurves of the plurality of typical terminals and obstacles and thevoltage corresponding to a distance point (Din+Dv); determining adetection voltage fluctuation range δ_(T) of the of the card caused by amobile terminal containing the card, the parameter δ_(T) representing afluctuation range of a detection voltage of the card caused byattenuation characteristics of the mobile terminal andδ_(T)=δ_(A)−δ_(R)−δ_(C); calculating a maximum field intensitydifference δ at various distances with distance control range of varioustypical terminals and obstacles; if δ is greater than δ_(T), decreasingthe frequency f and continuing from the step of determining thevoltage-distance curves; if δ is less than δ_(T), increasing thefrequency f and continuing from the step of determining thevoltage-distance curves; and if δ is equal to δ_(T), determining thecurrent frequency f is the frequency f0.
 8. The communication methodaccording to claim 2, wherein the modulation mode, the coding mode, andthe transmission magnetic flux density Bc of the first low-frequencyalternating magnetic field signal is selected by: selecting a codingmode without an average DC component; selecting no modulation or acarrier modulation mode without amplitude change; selecting thetransmission magnetic flux density Bc by: under a selected operatingfrequency that is less than f0, a selected modulation and a selectedcoding mode, selecting magnetic detection and the amplification gainthat are easy to achieve by the card reader; detecting an inherent noisevoltage amplitude Vn of the detection voltage of the card reader whenthere is no low-frequency alternating magnetic field signal; detectingthe detection voltage Vr of the card reader when the card reader issending the low-frequency alternating magnetic field signal using theselected modulation and coding mode; and selecting the transmissionmagnetic flux density Bc such that such that Vr/Vn>SNR, where SNR issignal-to-noise-ratio of the card reader. 9-13. (canceled)
 14. Thecommunication method according to claim 2, wherein: the one of the firstRF device and the second RF device sends a second low-frequencyalternating magnetic field signal to the other of the first RF deviceand the second RF device with communication distance confirmationinformation.
 15. The communication method according to claim 1, wherein:one of the first RF device and the second RF device sends a firstlow-frequency alternating magnetic field signal to the other of thefirst RF device and the second RF device, and receives a secondlow-frequency alternating magnetic field signal from the other of thefirst RF device and the second RF device; identification informationcarried in the second low-frequency alternating magnetic field signal isused to control communication distance between the first RF device andthe second RF device.
 16. (canceled)
 17. The communication methodaccording to claim 15, wherein: one of the first RF device and thesecond RF device converts the second low-frequency alternating magneticfield signal into a second electrical signal and compares the secondelectrical signal with a second preset threshold; and when the secondelectrical signal is greater than or equal to the second presetthreshold and the identification information in the second low-frequencyalternating magnetic field signal is the same as identificationinformation of the one of the first RF device and the second RF devicesending the first low-frequency alternating magnetic field signal, it isdetermined that the first RF device and the second RF device are withina valid distance range.
 18. The communication method according to claim15, wherein: the other of the first RF device and the second RF devicecontrols the communication distance between the first RF device and thesecond RF device based on received first low-frequency alternatingmagnetic field signal and, when it is considered that the first RFdevice and the second RF device are within a valid distance range, sendsback the second low-frequency alternating magnetic field signal.
 19. Thecommunication method according to claim 18, wherein the other of thefirst RF device and the second RF device controlling the communicationdistance between the first RF device and the second RF device based onreceived first low-frequency alternating magnetic field signal furtherincludes: converting the first low-frequency alternating magnetic fieldsignal into a first electrical signal; comparing the first electricalsignal with a first preset threshold value; and controlling thecommunication distance between the first RF device and second RF devicebased on a comparison result.
 20. (canceled)
 21. The communicationmethod according to claim 19, wherein: the first electrical signal is avoltage signal, the first threshold value is a voltage threshold Vt, andthe voltage threshold Vt is determined by: under selected transmissionparameters, measuring voltage-distance curves of a plurality of typicalterminals and obstacles, the selected transmission parameters includinga frequency of the low-frequency alternating magnetic field signal, amodulation mode, a coding mode, and a transmission magnetic flux densityBr; and obtaining a reference voltage-distance curve, the referencevoltage-distance curve being a average value of curves of the typicalterminals and obstacles; and selecting a voltage value at a distancepoint at half of a maximum valid card transaction range on the referencevoltage-distance curve as Vt for the card reader.
 22. The communicationmethod according to claim 18, wherein: the first RF device is a cardreader, the second RF device is a card, the first low-frequencyalternating magnetic field signal is related to a frequency f0 and, whena frequency of first low-frequency alternating magnetic field signal isless than or equal to the frequency f0, mobile terminals equipped withthe second RF device are within a valid distance range, the frequency f0is determined by: determining a distance control target (Din, Dv) basedon the first low-frequency alternating magnetic field signal, whereinDin represents a distance in which, within a range of 0-Din, cardtransaction is ensured for the mobile terminals equipped with the secondRF device, and Dv represents a distance fluctuation range in which,within Din˜(Din+Dv), card transaction is allowed and, beyond Din+Dv,card transaction is not allowed; determining a detection voltagefluctuation range δ_(R) of the second RF device caused by the first RFdevice; determining a detection voltage fluctuation range δ_(C) causedby the second RF device; determining voltage-distance curves of theplurality typical terminals and obstacles at the frequency f of firstlow-frequency alternating magnetic field signal; based on the distancecontrol target (Din, Dv), determining a detection voltage fluctuationrange δ_(A) of the second RF device, the range δ_(A) being equal to adifference between a voltage corresponding to a distance point Din on avoltage-distance curve with an average field intensity attenuation curveslope and obtained from the voltage-distance curves of the plurality oftypical terminals and obstacles and the voltage corresponding to adistance point (Din+Dv); determining a detection voltage fluctuationrange δ_(T) of the second RF device caused by a mobile terminalcontaining the second RF device, the parameter δ_(T) representing afluctuation range of a detection voltage of the card caused byattenuation characteristics of the mobile terminal andδ_(T)=δ_(A)−δ_(R)−δ_(C); calculating a maximum field intensitydifference δ at various distances with distance control range of varioustypical terminals and obstacles; if δ is greater than δ_(T), decreasingthe frequency f and continuing from the step of determining thevoltage-distance curves; if δ is less than δ_(T), increasing thefrequency f and continuing from the step of determining thevoltage-distance curves; and if δ is equal to δ_(T), determining thecurrent frequency f is the frequency f0.
 23. The communication methodaccording to claim 18, wherein: the first RF device is a card reader,the second RF device is a card, the second low-frequency alternatingmagnetic field signal is related to a frequency f0′ and, when afrequency of second low-frequency alternating magnetic field signal isless than or equal to the frequency f0′, mobile terminals equipped withthe second RF device are within a valid distance range, the frequencyf0′ is determined by: determining a distance control target (Din, Dv′)based on the second low-frequency alternating magnetic field signal,wherein Din represents a distance in which, within a range of 0-Din,card transaction is ensured for the mobile terminals equipped with thesecond RF device, and Dv′ represents a distance fluctuation range inwhich, within Din˜(Din+Dv′), card transaction is allowed and, beyondDin+Dv′, card transaction is not allowed; determining a detectionvoltage fluctuation range δ_(R) of the first RF device caused by thesecond RF device; determining a detection voltage fluctuation rangeδ_(C) caused by the first RF device; determining voltage-distance curvesof the plurality typical terminals and obstacles at the frequency f′ ofsecond low-frequency alternating magnetic field signal; based on thedistance control target (Din, Dv′), determining a detection voltagefluctuation range δ_(A)′ of the first RF device, the range δ_(A)′ beingequal to a difference between a voltage corresponding to a distancepoint Din on a voltage-distance curve with an average field intensityattenuation curve slope and obtained from the voltage-distance curves ofthe plurality of typical terminals and obstacles and the voltagecorresponding to a distance point (Din+Dv′); determining a detectionvoltage fluctuation range δ_(T)′ caused by a mobile terminal containingthe second RF device, the parameter δ_(T)′ representing a fluctuationrange of a detection voltage of the card caused by attenuationcharacteristics of the mobile terminal and δ_(T)′=δ_(A)′−δ_(R)′−δ_(C)′;and calculating a maximum field intensity difference δ′ at variousdistances with distance control range of various typical terminals andobstacles; if δ′ is greater than δ_(T)′, decreasing the frequency f andcontinuing from the step of determining the voltage-distance curves; ifδ′ is less than δ_(T)′, increasing the frequency f and continuing fromthe step of determining the voltage-distance curves; and if δ′ is equalto δ_(T)′, determining the current frequency f′ is the frequency f0′.24. The communication method according to claim 18, wherein themodulation mode, the coding mode, and the transmission magnetic fluxdensity Br of the first low-frequency alternating magnetic field signalis selected by: selecting a coding mode without an average DC component;selecting no modulation or a carrier modulation mode without amplitudechange; selecting the transmission magnetic flux density Br by: under aselected operating frequency that is less than f0, a selected modulationand a selected coding mode, selecting a typical noise mobile terminaland magnetic detection and the amplification gain that are easy toachieve in the second RF device; detecting an inherent noise voltageamplitude Vn of the detection voltage of the second RF device when thereis no low-frequency alternating magnetic field signal; detecting thedetection voltage Vc of the second RF device when the first RF device issending the low-frequency alternating magnetic field signal using theselected modulation and coding mode; and selecting the transmissionmagnetic flux density Br such that such that Vc/Vn>SNR, where SNR issignal-to-noise-ratio of the second RF device.
 25. (canceled) 26.(canceled)
 27. The communication method according to claim 24, whereinthe modulation mode, the coding mode, and the transmission magnetic fluxdensity Bc of the second low-frequency alternating magnetic field signalis selected by: selecting a coding mode without an average DC component;selecting no modulation or a carrier modulation mode without amplitudechange; selecting the transmission magnetic flux density Bc by: under aselected operating frequency that is less than f0′, the selectedmodulation and the selected coding mode, selecting a typical noiseterminal and magnetic detection and the amplification gain that are easyto achieve by the first RF device; detecting an inherent noise voltageamplitude Vn′ of the detection voltage of the first RF device when nolow-frequency alternating magnetic field signal; detecting the detectionvoltage Vr of the first RF device when the mobile terminal is sendingthe low-frequency alternating magnetic field signal using the selectedmodulation and coding mode; and selecting the transmission magnetic fluxdensity Bc such that such that Vr/Vn′>SNR′, where SNR′ issignal-to-noise-ratio of the first RF device. 28-33. (canceled)
 34. Aradio frequency (RF) device, comprising: a magnetic signal receivermodule configured to receive a first low-frequency alternating magneticfield signal of another RF device; a main control module configured tocontrol a communication distance between the RF device and the anotherRF device; and an RF transceiver module configured to exchange data withthe another RF device within a predetermined distance range.
 35. The RFdevice according to claim 34, wherein the main control module is furtherconfigured to: convert the first low-frequency alternating magneticfield signal into a first electrical signal; compare the firstelectrical signal with a first preset threshold value; and control thecommunication distance between the first RF device and second RF devicebased on a comparison result.
 36. The RF device according to claim 34,wherein: the magnetic signal receiver module includes an amplifiercircuit, a filter circuit, and a decoding circuit, sequentiallyconnected; the filter circuit is connected to a coupling coil in the RFdevice; and the decoding circuit is connected to the main controller,wherein: the amplifier circuit is configured to amplify a firstelectrical signal converted from the first low-frequency alternatingmagnetic field signal received by the coupling coil; the filter circuitis configured to filter the amplified first electrical signal and tosuppress noise and interference outside a valid signal frequency band;the decoding circuit is configured to decode the filtered signal basedon the coding mode of the RF device sending the first low-frequencyalternating magnetic field signal and to send the decoded signal to themain controller.
 37. The RF device according to claim 36, wherein themagnetic signal receiver module further includes: a demodulation circuitdisposed between the filter circuit and the decoding circuit andconfigured to demodulate the filtered signal based on a modulationscheme used by the another RF device and to send the demodulated signalto the decoding circuit.
 38. The RF device according to claim 34,wherein: the magnetic signal receiver module includes an amplifiercircuit and a filter circuit, sequentially connected; the filter circuitis connected to a coupling coil in the RF device; and the decodingcircuit is connected to the main controller, wherein: the amplifiercircuit is configured to amplify a first electrical signal convertedfrom the first low-frequency alternating magnetic field signal receivedby the coupling coil; the filter circuit is configured to filter theamplified first electrical signal and to suppress noise and interferenceoutside a valid signal frequency band; the main controller is furtherconfigured to decode the filtered signal based on the coding mode of theRF device sending the first low-frequency alternating magnetic fieldsignal.
 39. The RF device according to claim 38, the magnetic signalreceiver module further includes: a demodulation circuit disposedbetween the filter circuit and the main controller and configured todemodulate the filtered signal based on a modulation scheme used by theanother RF device and to send the demodulated signal to the maincontroller.
 40. The RF device according to claim 34, wherein: the RFtransceiver module includes an RF transceiver, an impedance matchingnetwork, and an RF antenna, sequentially connected, and the RFtransceiver is connected to the main controller.
 41. The RF deviceaccording to claim 34, further including: a magnetic signal transmittingmodule configured to transmit the communication distance confirmationinformation to the another RF device.
 42. The RF device according toclaim 41, wherein: the magnetic signal transmitting module includes anencoder circuit, a modulation circuit, a D/A converter circuit, and adrive circuit, sequentially connected, the encoder circuit is connectedto the main controller, and the drive circuit is connected to thecoupling coil in the RF device, wherein: the main controller isconfigured to generate information carried in the second low-frequencyalternating magnetic field signal to be transmitted by the RF device,the second low-frequency alternating magnetic field signal informationbeing a digital baseband signal; the encoder circuit is configured toencode the digital baseband signal provided by the main controller; theD/A converter circuit is configured to convert the encoded digitalsignal into a low-frequency analog signal; and the drive circuit isconfigured to amplify the low-frequency analog signal and to drive thecoupling coil to generate the second low-frequency alternating magneticfield.
 43. The RF device according to claim 42, wherein the magneticsignal transmitting module further includes: a modulation circuitdisposed between the main controller and the D/A converter circuit,wherein the modulation circuit is configured to modulate the encodeddata and to send the modulated data to the D/A converter circuit. 44.The RF device according to claim 42, wherein the magnetic signaltransmitting module further includes: a modulation circuit disposedbetween the main controller and the D/A converter circuit, wherein themodulation circuit is configured to modulate the encoded digitalbaseband signal and to send the modulated signal to the D/A convertercircuit.
 45. The RF device according to claim 41, wherein: the magneticsignal transmitting module includes a D/A converter circuit and a drivecircuit, sequentially connected, the D/A converter circuit is connectedto the main controller, and the drive circuit is connected to thecoupling coil in the RF device, wherein: the main controller isconfigured to generate low-frequency encoded data and to send the datato the D/A converter circuit; the D/A converter circuit is configured toconvert the low-frequency encoded data into a low-frequency analogsignal; and the drive circuit is configured to amplify the low-frequencyanalog signal and to drive the coupling coil to generate the secondlow-frequency alternating magnetic field.
 46. The RF device according toclaim 41, wherein: the magnetic signal receiver module and the magneticsignal transmitting module perform two-way communication with the RFdevice transmitting the first low-frequency alternating magnetic fieldsignal through a time-division duplex mode or a frequency-divisionduplex mode; and an operating frequency of the magnetic signal receivermodule and an operating frequency of the magnetic signal transmittingmodule both less than a predetermined maximum operating frequency.
 47. Acommunication system comprising a first radio frequency (RF) device andsecond RF device, wherein the first RF device and the second RF devicecontrol a communication distance using low-frequency alternatingmagnetic field signals and exchange information between the first RFdevice and the second RF device using RF channels, wherein: the first RFdevice further includes: a first magnetic signal transceiver configuredto generate and transmit a first low-frequency alternating magneticfield signal and to receive a second low-frequency alternating magneticfield signal; a first RF communication unit configured to exchangeinformation with the second RF device; the second RF device furtherincludes: a second magnetic signal transceiver configured to generateand transmit the second low-frequency alternating magnetic field signaland to receive the first low-frequency alternating magnetic fieldsignal; a second RF communication unit configured to exchangeinformation with the first RF communication unit.
 48. The communicationsystem according to claim 47, wherein: the first magnetic signaltransceiver further includes a first magnetic signal receiving unit anda first magnetic signal transmitting unit; the first magnetic signaltransmitting unit is configured to transmit the first low-frequencyalternating magnetic field signal; and the first magnetic signalreceiving unit is configured to receive the second low-frequencyalternating magnetic field signal; the second magnetic signaltransceiver further includes a second magnetic signal receiving unit anda second magnetic signal transmitting unit; the second magnetic signaltransmitting unit is configured to transmit the second low-frequencyalternating magnetic field signal; and the second magnetic signalreceiving unit is configured to receive the first low-frequencyalternating magnetic field signal.
 49. The communication systemaccording to claim 47, wherein: the first magnetic signal transceiverincludes a first modulation unit, and the first modulation unit isconfigured to add identification information of the first RF device intothe first low-frequency alternating magnetic field signal; and thesecond magnetic signal transceiver includes a second modulation unit,and the second modulation unit is configured to add identificationinformation of the second RF device into the second low-frequencyalternating magnetic field signal.
 50. The communication systemaccording to claim 49, wherein: the first magnetic signal transceiverincludes a first determination unit, and the first determination unit isconfigured to determine whether the first RF device enters into thepreset valid card transaction range between the second RF device and thefirst RF device, based on the second low-frequency alternating magneticfield signal detected by the first RF device; the second magnetic signaltransceiver includes a second determination unit, and the seconddetermination unit is configured to determine whether the second RFdevice enters into the preset valid card transaction range between thefirst RF device and the second RF device, based on the firstlow-frequency alternating magnetic field signal detected by the secondRF device; and when the second determination unit determines that thesecond RF device enters into the preset valid card transaction rangebetween the first RF device and the second RF device, and when the firstdetermination unit determines that the first RF device enters into thepreset valid card transaction range between the second RF device and thefirst RF device, it is determined that the distance between the first RFdevice and the second RF device is within the predetermined effectivecommunication distance range.
 51. The communication system according toclaim 50, wherein: the first determination unit includes a firstcomparison sub-unit and a first determination sub-unit, the firstcomparison sub-unit is configured to compare the identificationinformation of the first RF device demodulated from the secondlow-frequency alternating magnetic field signal with its ownidentification information; and the first determination sub-unit isconfigured to, based on a comparison result, determine whether the firstRF device enters into a predetermined valid distance range between thesecond RF device and the first RF device; and the second determinationunit includes a second comparison sub-unit and a second determinationsub-unit, the second comparison sub-unit is configured to compare theelectrical signal converted from the first low-frequency alternatingmagnetic field signal with the preset threshold value, and the seconddetermination sub-unit is configured to, based on a comparison result,determine whether the second RF device enters into a predetermined validdistance range between the second RF device and the first RF device. 52.The communication system according to claim 51, wherein: the firstjudgment unit includes a third comparison sub-unit and a thirddetermination sub-unit, the third comparison sub-unit is configured tocompare a second electrical signal converted from the secondlow-frequency alternating magnetic field signal with a second thresholdvalue, and the third determination sub-unit is configured to, based on acomparison result, determine whether the second RF device enters intothe predetermined valid distance range between the second RF device andthe first RF device.